staging: vchiq: Make creation of vchiq cdev optional

Before this commit, vchiq cdev (/dev/vchiq) was always created during
platform initialization. Introduce a new Kconfig option
CONFIG_VCHIQ_CDEV which determines if the cdev will be created or not.

Reviewed-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Ojaswin Mujoo <ojaswin98@gmail.com>
Link: https://lore.kernel.org/r/846c424dd4aae14d1cc28c8f30877a06e2b7dd10.1626882325.git.ojaswin98@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>