This extension has been superseded by SPV_KHR_cooperative_matrix which
is supported across major vendors GPU like Nvidia, AMD, and Intel.
Given that the KHR version has been supported for nearly half a year,
drop the NV-specific extension to reduce the maintenance burden and code
duplication.
Continue to work outlined in D155747 and split the main SPIR-V ops
implementation file into a few smaller and quicker to compile files.
This organization matches the op definition organizaion in `.td` files.
In this patch, extract atomic, cast/conversion, and group op
implementation into separate files.
Reviewed By: antiagainst
Differential Revision: https://reviews.llvm.org/D155777
