gfx: drv: fix exiting DSI ULPS mode during resume

gfx: drv: fix exiting DSI ULPS mode during resume

The DEVICE_READY_REG register used during resume to exit the ULPS mode
is pipe specific and we should use the already available
MIPI_DEVICE_READY_REG(pipe) macro to access it.

The current resume code calls mdfld_restore_display_registers for pipe A
and C, but due to the above bug will incorrectly exit ULPS mode in both
cases for pipe A. Fix this by exiting ULPS only on pipe A. For now this
works ok for tablets and for other devices the code was broken in the
first place anyway. Later we'll add a more generic solution to handle
ULPS state that works for other devices too.

Thanks for Jani Nikula for pointing this out.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>