irqchip/qcom-pdc: Switch to using IRQCHIP_PLATFORM_DRIVER helper macros

Switch the driver to use the helper macros. In addition to reducing the
number of lines, this also adds module unload protection (if the driver
is compiled as a module) by switching from module_platform_driver to
builtin_platform_driver.

Signed-off-by: Saravana Kannan <saravanak@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200718000637.3632841-3-saravanak@google.com