gdb, i386: Enable AVX512-bfloat16 for i386 targets.

gdb, i386: Enable AVX512-bfloat16 for i386 targets.

Values of type bfloat16 can also be used on 32-bit targets, which was missed
in the original enablement.  This also adjusts the testcase to pass with
"unix/-m32", where only the lower 8 AVX registers are available.

gdb/ChangeLog:
2021-07-21  Felix Willgerodt  <Felix.Willgerodt@intel.com>

	* features/i386/32bit-sse.xml: Add bfloat16 type.
	* features/i386/32bit-sse.c: Regenerated.

gdb/testsuite/ChangeLog:
2021-07-21  Felix Willgerodt  <Felix.Willgerodt@intel.com>

	* gdb.arch/x86-avx512bf16.exp: Only use x/z/ymm 0-7.