[LoongArch] Remove AssemblerPredicate for features: f/d/lsx/lasx/lvz/lbt

Linux LoongArch port [1] uses `-msoft-float` (implies no FPU) in its
`cflags` while it also uses floating-point insns in asm sources [2].
GAS allows this usage while IAS currently does not.

This patch removes `AssemblerPredicate`s for floating-point insns so
that to make IAS compitable with GAS. Similarly, also remove
`AssemblerPredicate`s for other ISA extensions, i.e. lsx/las/lvz/lbt.

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/loongarch/Makefile?h=v6.4-rc1#n49
[2]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/loongarch/kernel/fpu.S?h=v6.4-rc1#n29

Reviewed By: xen0n, hev

Differential Revision: https://reviews.llvm.org/D150196