drm: call drm client for bootsplash entry

call drm_bootsplash_client_register() from drm_client_dev_register()
to enable bootsplash support.

Change-Id: I2c862f8520aacd380340301679c4b825c755c44a
Signed-off-by: Shubham Talekar <stalek@codeaurora.org>