Move framebuffer vmap code from shadow-buffered plane state into the new
interfaces drm_gem_fb_vmap() and drm_gem_fb_vunmap(). These functions
provide mappings of a framebuffer's BOs into kernel address space. No
functional changes.
v4:
* remove duplicated blank line
v2:
* using [static N] for array parameters enables compile-time checks
* include <drm/drm_fourcc.h> for DRM_FORMAT_MAX_PLANES (kernel
test robot)