aarch64: Use force_lowpart_subreg in a BFI splitter [PR119133]

aarch64: Use force_lowpart_subreg in a BFI splitter [PR119133]

lowpart_subreg ICEs are the gift that keeps giving.  This is another
case where we need to use force_lowpart_subreg instead, to handle
cases where the input is already a subreg and where the combined
subreg is not allowed as a single operation.

We don't need to check can_create_pseudo_p since the input should
be a hard register rather than a subreg if !can_create_pseudo_p.

gcc/
	PR target/119133
	* config/aarch64/aarch64.md
	(*aarch64_bfi<GPI:mode><ALLX:mode>_<SUBDI_BITS>): Use
	force_lowpart_subreg.

gcc/testsuite/
	PR target/119133
	* gcc.dg/torture/pr119133.c: New test.