drm/exynos: unify exynos_drm_plane names with drm core

Rename crtc_{widht,height} to crtc_{w,h} and src_{width,height} to
src_{w,h} to make it similar to the atomic state names.

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Reviewed-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>