media: ov5647: Remove 640x480 SBGGR8 mode

Capturing in 640x480 SBGGR8_1X8 hangs the system when capturing
with the unicam driver on RaspberryPi 4 platform.

Remove it and remove the support for multiple media bus codes in
the driver.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>