ARM: riscpc: move time-acorn.c to mach-rpc

Nothing but RiscPC makes use of the Acorn timekeeping code, so move
it into mach-rpc.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/common/Kconfig

@@ -35,9 +35,6 @@ config DMABOUNCE
 	bool
 	select ZONE_DMA
 
-config TIMER_ACORN
-	bool
-
 config SHARP_LOCOMO
 	bool