mips: msa: truncate immediate shift amount [PR101922]

mips: msa: truncate immediate shift amount [PR101922]

When -mloongson-mmi is enabled, SHIFT_COUNT_TRUNCATED is turned off.
This causes untruncated immediate shift amount outputed into the asm,
and the GNU assembler refuses to assemble it.

Truncate immediate shift amount when outputing the asm instruction to
make GAS happy again.

gcc/

	PR target/101922
	* config/mips/mips-protos.h (mips_msa_output_shift_immediate):
	  Declare.
	* config/mips/mips.c (mips_msa_output_shift_immediate): New
	  function.
	* config/mips/mips-msa.md (vashl<mode>3, vashr<mode>3,
	  vlshr<mode>3): Call it.

gcc/testsuite/

	PR target/101922
	* gcc.target/mips/pr101922.c: New test.