[mlir][amx] Add Intel AMX dialect (architectural-specific vector dialect)

The Intel Advanced Matrix Extensions (AMX) provides a tile matrix
multiply unit (TMUL), a tile control register (TILECFG), and eight
tile registers TMM0 through TMM7 (TILEDATA). This new MLIR dialect
provides a bridge between MLIR concepts like vectors and memrefs
and the lower level LLVM IR details of AMX.

Reviewed By: nicolasvasilache

Differential Revision: https://reviews.llvm.org/D98470