drivers: pinmux: stm32: Add support for STM32F302x8
drivers: pinmux: stm32: Add support for STM32F302x8

Add pin muxing for STM32F302x8 by sharing most of the definitions
of the STM32F303xC.  Add USART3 for both the 302x8 and the 303xC.
Add a PWM that is specific to the 302x8.

Signed-off-by: Galen Seitz <4b943fd5fb6f9590458eea94d3310f73210856ae@seitzassoc.com>

nashif/zephyr,Vudentz/zephyr,nashif/zephyr,nashif/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,punitvara/zephyr,nashif/zephyr,explora26/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,Vudentz/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,punitvara/zephyr,explora26/zephyr,punitvara/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,finikorg/zephyr,punitvara/zephyr,explora26/zephyr,galak/zephyr,galak/zephyr,Vudentz/zephyr,galak/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,ldts/zephyr,finikorg/zephyr