pinctrl: renesas: rmobile: Mark unused PORTCR bits reserved

The PULMD bits and the SEC bit in the PORTCR register descriptions on
SH/R-Mobile SoCs are either unused or unsupported.  Describe them as
reserved bits using a negative field width value, and drop the
corresponding dummy enum IDs.

This reduces kernel size by 2832 (R-Mobile APE6), 2544 (R-Mobile A1),
and/or 3228 (SH-Mobile AG5) bytes.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/1b123d8f04c2314d5a7a87004971868ba2176499.1649865241.git.geert+renesas@glider.be