drm/xe: Extend rpX values extraction for future platforms

In existing code flow for future platforms i.e. >1270, the rpX
(rp0,rpn and rpe) fused values are read from gen 6 registers.
Which is not correct. Unless specified gen 1270 regs should be valid
for gen 1270+ platforms as well.

Signed-off-by: Badal Nilawar <badal.nilawar@intel.com>
Reviewed-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>