soc: sifive: replace SOC_FOO with ARCH_FOO

As part of unifiying what RISC-V calls microarch symbols to use
ARCH_, replace users of the SOC_ forms.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

drivers/soc/sifive/Kconfig

@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 
-if SOC_SIFIVE || SOC_STARFIVE
+if ARCH_SIFIVE || ARCH_STARFIVE
 
 config SIFIVE_CCACHE
 	bool "Sifive Composable Cache controller"