Update regDefs.h

Update ZZ(PCISPC_PXLCAP MaskRO from 0x00000000fff7ffff to 0x00000000ffffffff 
Update ZZ(PCISPC_PXLCAP ImplSpec from 0x00000000ff07ffff to 0x00000000ff47ffff 
Refer to Spec section 2.6.5.