irqchip/stm32: Add usart instances exti direct event support

irqchip/stm32: Add usart instances exti direct event support

Add following usart instances exti direct event support (used for UART wake
up).
- exti 26 (USART1) is mapped to GIC 37
- exti 27 (USART2) is mapped to GIC 38
- exti 28 (USART3) is mapped to GIC 39
- exti 29 (USART6) is mapped to GIC 71
- exti 31 (UART5) is mapped to GIC 53
- exti 32 (UART7) is mapped to GIC 82
- exti 33 (UART8) is mapped to GIC 83

Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210319184253.5841-4-erwan.leray@foss.st.com