staging: vchiq: Add details to Kconfig help texts

Add some details to the Kconfig definitions of $CONFIG_VCHIQ_CDEV and
$CONFIG_BCM2835_VCHIQ to help make the motive behind the configs a bit
more clear.

Reviewed-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Ojaswin Mujoo <ojaswin98@gmail.com>
Link: https://lore.kernel.org/r/ab88d3222088aca29a319147b50a9d1e9f0f8b81.1627925241.git.ojaswin98@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>