drm/i915/psr: Set frames before SU entry for psr2

drm/i915/psr: Set frames before SU entry for psr2

Set frames before SU entry value for max resync frame count of
dpcd register 2009, bit field 0:3.

v2 :
 - add macro  EDP_PSR2_FRAME_BEFORE_SU (Rodrigo)
 - remove EDP_FRAMES_BEFORE_SU_ENTRY (Rodrigo)
 - add check ==1 for dpcd_read call (ville)

v3 : (Rodrigo)
 - move macro EDP_PSR2_FRAME_BEFORE_SU after EDP_PSR2_FRAME_BEFORE_SU
 - replace with &=

v4 :
 - change the macro to shift value (jani)
 - updated register names

Cc: Rodrigo Vivi <[email protected]>
CC: Puthikorn Voravootivat <[email protected]>
Reviewed-by: Rodrigo Vivi <[email protected]>
Signed-off-by: Vathsala Nagaraju <[email protected]>
Signed-off-by: Rodrigo Vivi <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]