misc: bcm-vk: add VK messaging support

Add message support in order to be able to communicate
to VK card via message queues.

This info is used for debug purposes via collection of logs via direct
read of BAR space and by sysfs access (in a follow on commit).

Co-developed-by: Desmond Yan <desmond.yan@broadcom.com>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Desmond Yan <desmond.yan@broadcom.com>
Signed-off-by: Scott Branden <scott.branden@broadcom.com>
Link: https://lore.kernel.org/r/20210120175827.14820-10-scott.branden@broadcom.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>