drm/mgag200: Include <linux/vmalloc.h> for G200 BIOS code

After moving the vmalloc() call to another file, the rsp include
statement needs to be moved as well. Resolves a build warning on
parisc.

 drivers/gpu/drm/mgag200/mgag200_g200.c: In function
	'mgag200_g200_init_refclk':
 drivers/gpu/drm/mgag200/mgag200_g200.c:120:16: error: implicit
	declaration of function 'vmalloc'; did you mean 'kvmalloc'?
	[-Werror=implicit-function-declaration]

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 85397f6b

 ("drm/mgag200: Initialize each model in separate function")
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reported-by: kernel test robot <lkp@intel.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Jocelyn Falempe <jfalempe@redhat.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Link: https://lore.kernel.org/all/202206080734.ztAvDG7O-lkp@intel.com/
Link: https://patchwork.freedesktop.org/patch/msgid/20220608115122.7448-1-tzimmermann@suse.de