LDS block size should be 2048 bytes (512 dwords) based on current spec.

AMDGPUMCExpr lives in the MC layer it should not depend on Function.h or
GCNSubtarget.h

Move the function that needed GCNSubtarget to the one file that called
it.

This reverts commit be17791f2624f22b3ed24a2539406164a379125d.

This is not necessary for gfx1250 anymore.

According to `llvm-project/llvm/docs/AMDGPUUsage.rst::L5212` the
`GRANULATED_WAVEFRONT_SGPR_COUNT`, which is `compute_pgm_rsrc1[6:9]` has
to be 0 for gfx10+ arch

---------

Co-authored-by: Matt Arsenault <Matthew.Arsenault@amd.com>

COMPUTE_PGM_RSRC3 does exist on gfx1250, we are just not using it yet.

getAddressableLocalMemorySize() already returns unsigned.

For each function with the AMDGPU_CS_Chain calling convention, with
dynamic VGPRs enabled, add a _dvgpr$ symbol, with the value of the
function symbol, plus an offset encoding one less than the number of
VGPR blocks used by the function (16 VGPRs per block, no more than 128)
in bits 5..3 of the symbol value. This is used by a front-end to have
functions that are chained rather than called, and a dispatcher that
dynamically resizes the VGPR count before dispatching to a function.