Change serial irq to rising edge.
Change serial irq to rising edge.

Use the device tree clock node definition (apb_pclk).

Signed-off-by: Andrei Sandu <dbc21552912e46b041d86cfb2348c8cc4a9bf089@amazon.com>

firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker