[AMDGPU][MC] Added support of SP3 syntax for MTBUF format modifier

[AMDGPU][MC] Added support of SP3 syntax for MTBUF format modifier

Currently supported LLVM MTBUF syntax is shown below. It is not compatible with SP3.

    op     dst, addr, rsrc, FORMAT, soffset

This change adds support for SP3 syntax:

    op     dst, addr, rsrc, soffset SP3FORMAT

In addition to being compatible with SP3, this syntax allows using symbolic names for data, numeric and unified formats. Below is a list of added syntax variants.

format:<expression>
format:[<numeric-format-name>,<data-format-name>]
format:[<data-format-name>,<numeric-format-name>]
format:[<data-format-name>]
format:[<numeric-format-name>]
format:[<unified-format-name>]

The last syntax variant is supported for GFX10 only.

See llvm bug 37738

Reviewers: arsenm, rampitec, vpykhtin

Differential Revision: https://reviews.llvm.org/D84026