media: uapi: pisp_be_config: Drop BIT() from uAPI

The pisp_be_config.h uAPI header file contains a bit-field definition
that uses the BIT() helper macro.

As the BIT() identifier is not defined in userspace, drop it from the
uAPI header.

Fixes: c6c49bac ("media: uapi: Add Raspberry Pi PiSP Back End uAPI")
Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>