staging: vc04_services: Move global memory mapped pointer

g_regs stores the remapped memory pointer for the vchiq platform.
It can be moved to struct vchiq_drv_mgmt instead of being global.

Adjust the affected functions accordingly. Pass vchiq_state pointer
wherever necessary to access struct vchiq_drv_mgmt.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
Link: https://lore.kernel.org/r/20240412075743.60712-8-umang.jain@ideasonboard.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>