video: fbdev: wmt_ge_rops: Fix function not declared warnings

Include own header to fix "function not declared" warnings.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Tony Prisk <linux@prisktech.co.nz>
Cc: linux-arm-kernel@lists.infradead.org
Link: https://patchwork.freedesktop.org/patch/msgid/20201206190247.1861316-9-sam@ravnborg.org