ARM: dts: stm32: use dedicated files to manage stm32mp157 packages

ARM: dts: stm32: use dedicated files to manage stm32mp157 packages

Four packages exist for stm32mp157 die. As ball-out is different between
them, this patch covers those differences by creating dedicated pinctrl
dtsi files. Each dtsi pinctrl package file describes the package ball-out
through gpio-ranges.

stm32mp157a-dk1 / dk2 boards embed a STM32MP_PKG_AC (TFBGA361 (12*12))
package.

stm32mp157c-ed1 / ev1 boards embed a STM32MP_PKG_AA (LFBGA448 (18*18))
package.

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