[X86] [AMX] Replace bitcast with specific AMX intrinsics with X86 specific cast.

There is some discussion on the bitcast for vector and x86_amx at https://reviews.llvm.org/D99152. This patch is to introduce a x86 specific cast for vector and x86_amx, so that it can avoid some unnecessary optimization by middle-end. On the other way, we have to optimize the x86 specific cast by ourselves. This patch also optimize the cast operation to eliminate redundant code.

Reviewed By: LuoYuanke

Differential Revision: https://reviews.llvm.org/D107544