drm/i915/sdvo: Shrink sdvo_cmd_names[] strings

Drop the redundant "SDVO_CMD_" prefix from the command name
strings in sdvo_cmd_names[].

While at it throw away the unused struct name, and undef
SDVO_CMD_NAME_ENTRY() when we're done.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190619180312.31817-4-ville.syrjala@linux.intel.comReviewed-by: Chris Wilson <chris@chris-wilson.co.uk>