[AMDGPU][MC][True16] Rename and combine VINTERP MC tests (#85949)

NFC.
gfx11_asm_vinterp.s already contained GFX12 run lines. Rename the
assembler and disassembler tests to be sorted based on real16 or fake16
instead of gfxip. Note, both GFX11 and GFX12 currently only have fake16
(fake16 in encoding, but not by name) upstream, so that is why the test
files have a -fake16 suffix.

One test input is changed, and that is the disassembler test for
unsupported bits in the instruction. It is now an input that is valid on
both GFX11 and GFX12. This was necessary because the size of the opcode
field changed.

Author: Sisyph