PCI: dwc: Convert SOC_SIFIVE to ARCH_SIFIVE

As part of converting RISC-V SOC_FOO symbols to ARCH_FOO to match the
use of such symbols on other architectures, convert the SiFive PCI
drivers to use the newer symbol.

Link: https://lore.kernel.org/linux-pci/20230918-safeness-cornflake-62278bc3aaaa@wendy


Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>