drm/i915/psr: Clean up PSR register defininitions

Use REG_BIT() & co. to make the PSR register definitions
nicer.

v2: Rebase due to intel_psr_regs.h

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230411191429.29895-4-ville.syrjala@linux.intel.com


Reviewed-by: Jouni Högander <jouni.hogander@intel.com>