clk: microchip: core: allow driver to be compiled with COMPILE_TEST

clk: microchip: core: allow driver to be compiled with COMPILE_TEST

This driver currently only supports builds against a PIC32 target. To
avoid future breakage in the future, let's update the Kconfig and the
driver so that it can be built with CONFIG_COMPILE_TEST enabled.

Note that with the existing asm calls is not how I'd want to do this
today if this was a new driver, however I don't have access to this
hardware. To avoid any breakage, let's keep the existing behavior.

Signed-off-by: Brian Masney <bmasney@redhat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>