drm/tilcdc: request and mapp iomem with devres

tilcdc currently just ioremaps its iomem, without doing the (a bit more
robust) request on the memory first. The devm_ functions provide a handy
way to both request and ioremap the memory with automatic cleanup.

Replace the manual ioremap with the devm_ version.

Suggested-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Philipp Stanner <pstanner@redhat.com>
Reviewed-by: Jyri Sarha <jyri.sarha@iki.fi>
Tested-by: Jyri Sarha <jyri.sarha@iki.fi>
Signed-off-by: Jyri Sarha <jyri.sarha@iki.fi>
Link: https://patchwork.freedesktop.org/patch/msgid/20231222115216.19218-2-pstanner@redhat.com