Fix internal error with vectorization on SPARC

Fix internal error with vectorization on SPARC

This is a regression present since the 10.x series, but the underlying issue
has been there since the TARGET_VEC_PERM_CONST hook was implemented, in the
form of an ICE when expanding a constant VEC_PERM_EXPR in V4QI, while the
back-end only supports V8QI constant VEC_PERM_EXPRs.

gcc/
	PR target/105292
	* config/sparc/sparc.cc (sparc_vectorize_vec_perm_const): Return
	true only for 8-byte vector modes.

gcc/testsuite/
	* gcc.target/sparc/20220510-1.c: New test.