drm/i915/sdvo: Use named initializers for the SDVO command names

drm/i915/sdvo: Use named initializers for the SDVO command names

Use named initializers to make it easier to associate the SDVO debug
prints with the SDVO command defines. Also switch to using ARRAY_SIZE()
instead of assuming that SDVO_CMD_STATUS_SCALING_NOT_SUPP is the last
command type.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190619180312.31817-2-ville.syrjala@linux.intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>