Reland [AMDGPU] New PAL metadata updates to ps_extra_lds_size and float_mode

New metadata format contains full calculation of field contents for
ps_extra_lds_size (vs old format where the value in RSRC register is used by PAL
to calculate the value required).

Also stop updating float_mode and rely on front end settings for this field.

Differential Revision: https://reviews.llvm.org/D152247