pinctrl: sh-pfc: rcar-gen3: Remove HDMI CEC pins, groups, and functions

The HDMI CEC function is not supported by the R-Car Gen3 Hardware Manual
Rev 1.00. Therefore, delete the corresponding pin groups and functions,
and rename the HDMI[01]_CEC definitions to match their GPIO
functionality.

Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
[geert: Squashed several commits]
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>