soc/tegra: pmc: Select GENERIC_PINCONF

I have hit the following build error:
armv7a-hardfloat-linux-gnueabi-ld: drivers/soc/tegra/pmc.o: in function `pinconf_generic_dt_node_to_map_pin':
pmc.c:(.text+0x500): undefined reference to `pinconf_generic_dt_node_to_map'
armv7a-hardfloat-linux-gnueabi-ld: drivers/soc/tegra/pmc.o:(.rodata+0x1f88): undefined reference to `pinconf_generic_dt_free_map'

So SOC_TEGRA_PMC should select GENERIC_PINCONF.

Fixes: 4a37f11c ("soc/tegra: pmc: Implement pad configuration via pinctrl")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>