staging: vchiq: Move certain declarations to vchiq_arm.h

Move certain declarations from vchiq_arm.c to vchiq_arm.h to allow
code sharing. This will be useful when we eventually separate the vchiq
char driver code from platform code, into its own file.

Reviewed-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Ojaswin Mujoo <ojaswin98@gmail.com>
Link: https://lore.kernel.org/r/8abcbd9fb3227e2a78ccc4a1186c8c0801061a68.1626882325.git.ojaswin98@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>