LoongArch: Fix incorrect reorder of __lsx_vldx and __lasx_xvldx [PR119084]

LoongArch: Fix incorrect reorder of __lsx_vldx and __lasx_xvldx [PR119084]

They could be incorrectly reordered with store instructions like st.b
because the RTL expression does not have a memory_operand or a (mem)
expression.  The incorrect reorder has been observed in openh264 LTO
build.

Expand them to a (mem) expression instead of unspec to fix the issue.

Closes: https://github.com/cisco/openh264/issues/3857
(cherry picked from commit 4856292f7a680ec478e7607f1b71781996d7d542)

Edited to remove the loongarch.cc change which is not needed for gcc-14
branch.

gcc/ChangeLog:

	PR target/119084
	* config/loongarch/lasx.md (UNSPEC_LASX_XVLDX): Remove.
	(lasx_xvldx): Remove.
	* config/loongarch/lsx.md (UNSPEC_LSX_VLDX): Remove.
	(lsx_vldx): Remove.
	* config/loongarch/simd.md (QIVEC): New define_mode_iterator.
	(<simd_isa>_<x>vldx): New define_expand.

gcc/testsuite/ChangeLog:

	PR target/119084
	* gcc.target/loongarch/pr119084.c: New test.