[APX] i386: Fix illegal broadcast instruction generated by intrinsic

[APX] i386: Fix illegal broadcast instruction generated by intrinsic

For _mm256_broadcastsi128_si256 call with -mapxf enabled it may produce
illegal vbroadcasti128 with egpr under high register pressure. Restrict
the pattern to use "jm" and gpr16 for avx2 alternative.

gcc/ChangeLog:

	* config/i386/sse.md (avx2_vbroadcasti128_<mode>): Constraint
	alternative 0 with jm and add gpr16 attr to avoid egpr usage.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/apx-broadcast.c: New test.