aarch64: Add an and/ior-based movk pattern [PR87763]

aarch64: Add an and/ior-based movk pattern [PR87763]

This patch adds a second movk pattern that models the instruction
as a "normal" and/ior operation rather than an insertion.  It fixes
the third insv_1.c failure in PR87763, which was a regression from
GCC 8.

2020-02-06  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	PR target/87763
	* config/aarch64/aarch64-protos.h (aarch64_movk_shift): Declare.
	* config/aarch64/aarch64.c (aarch64_movk_shift): New function.
	* config/aarch64/aarch64.md (aarch64_movk<mode>): New pattern.

gcc/testsuite/
	PR target/87763
	* gcc.target/aarch64/movk_2.c: New test.