i386: Mark XMM4-XMM6 as clobbered by encodekey128/encodekey256

i386: Mark XMM4-XMM6 as clobbered by encodekey128/encodekey256

encodekey128 and encodekey256 operations clear XMM4-XMM6.  But it is
documented that XMM4-XMM6 are reserved for future usages and software
should not rely upon them being zeroed.  Change encodekey128 and
encodekey256 to clobber XMM4-XMM6.

gcc/

	PR target/107061
	* config/i386/predicates.md (encodekey128_operation): Check
	XMM4-XMM6 as clobbered.
	(encodekey256_operation): Likewise.
	* config/i386/sse.md (encodekey128u32): Clobber XMM4-XMM6.
	(encodekey256u32): Likewise.

gcc/testsuite/

	PR target/107061
	* gcc.target/i386/keylocker-encodekey128.c: Don't check
	XMM4-XMM6.
	* gcc.target/i386/keylocker-encodekey256.c: Likewise.

(cherry picked from commit db288230db55dc1ff626f46c708b555847013a41)