drm/i915/psr: Add bits per pixel limitation

PSR2 HW only support a limited number of bits per pixel, if mode has
more than supported PSR2 should not be enabled.

BSpec: 50422
BSpec: 7713
Cc: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191128014852.214135-1-jose.souza@intel.com