[AMDGPU] Update SPI_SHADER_PGM_RSRC2_PS.EXTRA_LDS_SIZE for GFX11

The granularity of SPI_SHADER_PGM_RSRC2_PS.EXTRA_LDS_SIZE changed
in GFX11. It is now in units of 256 dwords instead of 128 dwords.

COMPUTE_PGM_RSRC2.LDS_SIZE is unaffected. It is still in units of
128 dwords.

Differential Revision: https://reviews.llvm.org/D128179