pinctrl: stm32: introduce package support

A same SoC can be available in several packages. Differences between
packages are only the numbers of available balls. In order not to write
a driver for each new package, same driver (ex: pinctrl-stm32mp157.c) will
be used. This patch introduces the "package" property for each pin. So on a
same driver, it will be possible to indicate on which package the pin is
available. The package information will be got from the device tree.

Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>