drivers/pl011: ACPI: The interrupt should always be high level triggered

drivers/pl011: ACPI: The interrupt should always be high level triggered

The SPCR does not specify if the interrupt is edge or level triggered.
So the configuration needs to be hardcoded in the code.

Based on the PL011 TRM (see 2.2.8 in ARM DDI 0183G), the interrupt generated
will be active high. Whilst the wording may be interpreted differently,
the SBSA (section 4.3.2 in ARM-DEN-0029 v2.3) states the PL011 is
implemented with a level triggered interrupt.

So the driver should configure the interrupt as high level triggered.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Shannon Zhao <shannon.zhao@linaro.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>