Fix SVE-related failure in gdb.arch/aarch64-fp.exp

Fix SVE-related failure in gdb.arch/aarch64-fp.exp

The gdb.arch/aarch64-fp.exp test assumes it is dealing with a regular SIMD
target that exposes the V registers as raw registers.  SVE-enabled targets
turn the V registers into pseudo-registers.

That is all fine, but the testcase uses the "info registers" command, which
prints pseudo-register's contents twice. One for the hex format and another
for the natural format of the type.

(gdb) info registers v0
v0             {d = {f = {0x0, 0x0}, u = {0x1716151413121110, 0x1f1e1d1c1b1a1918}, s = {0x1716151413121110, 0x1f1e1d1c1b1a1918}}, s = {f = {0x0, 0x0, 0x0, 0x0}, u = {0x13121110, 0x17161514, 0x1b1a1918, 0x1f1e1d1c}, s = {0x13121110, 0x17161514, 0x1b1a1918, 0x1f1e1d1c}}, h = {f = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}, u = {0x1110, 0x1312, 0x1514, 0x1716, 0x1918, 0x1b1a, 0x1d1c, 0x1f1e}, s = {0x1110, 0x1312, 0x1514, 0x1716, 0x1918, 0x1b1a, 0x1d1c, 0x1f1e}}, b = {u = {0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f}, s = {0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f}}, q = {u = {0x1f1e1d1c1b1a19181716151413121110}, s = {0x1f1e1d1c1b1a19181716151413121110}}} {d = {f = {1.846323925681849e-197, 8.5677456166123577e-159}, u = {1663540288323457296, 2242261671028070680}, s = {1663540288323457296, 2242261671028070680}}, s = {f = {1.84362032e-27, 4.84942184e-25, 1.27466897e-22, 3.34818801e-20}, u = {319951120, 387323156, 454695192, 522067228}, s = {319951120, 387323156, 454695192, 522067228}}, h = {f = {0.00061798, 0.00086308, 0.0012398, 0.00173, 0.0024872, 0.0034676, 0.0049896, 0.0069504}, u = {4368, 4882, 5396, 5910, 6424, 6938, 7452, 7966}, s = {4368, 4882, 5396, 5910, 6424, 6938, 7452, 7966}}, b = {u = {16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31}, s = {16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31}}, q = {u = {41362427191743139026751447860679676176}, s = {41362427191743139026751447860679676176}}}

(gdb) p/x $v0
$1 = {d = {f = {0x0, 0x0}, u = {0x1716151413121110, 0x1f1e1d1c1b1a1918}, s = {0x1716151413121110, 0x1f1e1d1c1b1a1918}}, s = {f = {0x0, 0x0, 0x0, 0x0}, u = {0x13121110, 0x17161514, 0x1b1a1918, 0x1f1e1d1c}, s = {0x13121110, 0x17161514, 0x1b1a1918, 0x1f1e1d1c}}, h = {f = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}, u = {0x1110, 0x1312, 0x1514, 0x1716, 0x1918, 0x1b1a, 0x1d1c, 0x1f1e}, s = {0x1110, 0x1312, 0x1514, 0x1716, 0x1918, 0x1b1a, 0x1d1c, 0x1f1e}}, b = {u = {0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f}, s = {0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f}}, q = {u = {0x1f1e1d1c1b1a19181716151413121110}, s = {0x1f1e1d1c1b1a19181716151413121110}}}

Since the testcase is not expecting that, we run into a couple failures:

FAIL: gdb.arch/aarch64-fp.exp: check register v0 value
FAIL: gdb.arch/aarch64-fp.exp: check register v1 value

The following patch switches to using "p/x" for printing register values, which
prints the values once with the hex format, instead of twice.

gdb/testsuite/ChangeLog

2020-02-28  Luis Machado  <luis.machado@linaro.org>

	* gdb.arch/aarch64-fp.exp: Switch from "info registers" command
	to "p/x".