pinctrl: zynqmp: Support muxing individual pins

While muxing groups of pins at once can be convenient for large
interfaces, it can also be rigid. This is because the group is set to
all pins which support a particular function, even though not all pins
may be used. For example, the sdhci0 function may be used with a 8-bit
eMMC, 4-bit SD card, or even a 1-bit SD card. In these cases, the extra
pins may be repurposed for other uses, but this is not currently
allowed.

There is not too much point in pin "groups" when there are not actual
pin groups at the hardware level. The pins can all be muxed
individually, so there's no point in adding artificial groups on top.
Just mux the pins like the hardware allows.

To this effect, add a new group for each pin which can be muxed. These
groups are part of each function the pin can be muxed to. We treat group
selectors beyond the number of groups as "pin" groups. To set this up,
we initialize groups before functions, and then create a bitmap of used
pins for each function. These used pins are appended to the function's
list of groups.

Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
Reviewed-by: Sai Krishna Potthuri <sai.krishna.potthuri@amd.com>
Acked-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/20240610223550.2449230-3-sean.anderson@linux.dev
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

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