Provide drm_fb_blit() that works with struct iosys_map. Update all
users of drm_fb_blit_toio(), which required a destination buffer in
I/O memory.

This patch only updates the function's interface. The implementation
still relies on the destination buffer to be located in  I/O memory.
See the follow-up patches for implementational changes. The new
function's interface works with multi-plane color formats, but again
implementation only supports a single plane for now.

v2:
	* rebase onto refactored simpledrm
	* use IOSYS_MAP_INIT_VADDR() (Sam)
	* update the commit message on the use of I/O memory (Sam)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220808125406.20752-3-tzimmermann@suse.de