freedreno/a6xx: Fix CP_BIN_SIZE_ADDRESS name
It's actually for MEM_READ_ADDR, however I took the ST name from the a3xx docs. Also document some other registers gleaned from looking at the context switch save/restore routines and fix CP_SDS_REM_SIZE. Note that the CP reads the draw stream size in CP_SET_BIN_DATA5 using MEM_READ_ADDR, which is probably why this was mistaken for the draw stream size address.