pinctrl: stm32: Introduce HDP driver

This patch introduce the driver for the Hardware Debug Port available on
STM32MP platforms. The HDP allows the observation of internal SoC
signals by using multiplexers. Each HDP port can provide up to 16
internal signals (one of them can be software controlled as a GPO).

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Clément Le Goffic <clement.legoffic@foss.st.com>
Link: https://lore.kernel.org/20250711-hdp-upstream-v7-2-faeecf7aaee1@foss.st.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>