irqchip/stm32-exti: Add all LP timer exti direct events support

Add all remaining LP timer exti direct events, e.g. for LP Timer 2 to 5.
LP timer 1 is already listed (e.g. exti 47).

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/1602859219-15684-2-git-send-email-fabrice.gasnier@st.com