rtc: mpfs: convert SOC_MICROCHIP_POLARFIRE to ARCH_MICROCHIP_POLARFIRE

As part of converting RISC-V SOC_FOO symbols to ARCH_FOO to match the
use of such symbols on other architectures, convert the Microchip FPGA
RTC driver to use the new symbol.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230309204452.969574-5-conor@kernel.org


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>