Putting the complex condition in a variable does not help readability.
It is simpler to use separate `if`s.

When iterating over a block, meta instructions have no effect on wait counts,
but their presence drops the reference to earlier waitcnt instructions before
they are processed. This results in spurious wait counts, which do not affect
correctness, but are also not required in the resulting program. Skipping meta
instructions as soon as they are seen cleans this up.

This patch tracks the register operands of both VMEM (FLAT, MUBUF,
MTBUF) and SMEM load-store operations and inserts a S_WAIT_XCNT
instruction with sufficient wait-count before potentially redefining
them. For VMEM instructions, XNACK is returned in the same order as
they were issued and hence non-zero counter values can be inserted.
However, SMEM execution is out-of-order and so is their XNACK reception.
Thus, only zero counter value can be inserted to capture SMEM dependencies.

Use a function attribute (amdgpu-dynamic-vgpr) instead of a subtarget
feature, as requested in #130030.