ARM: at91: switch configuration option to SOC_AT91RM9200

As the ARCH_AT91RM9200 is removed because being !DT, we use
the SOC_AT91RM9200 variant. This option can certainly be removed
once the ST driver is reworked a bit.
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Boris BREZILLON <boris.brezillon@free-electrons.com>

arch/arm/mach-at91/Kconfig

@@ -224,7 +224,7 @@ config AT91_TIMER_HZ
        int "Kernel HZ (jiffies per second)"
        range 32 1024
        depends on ARCH_AT91
-       default "128" if ARCH_AT91RM9200
+       default "128" if SOC_AT91RM9200
        default "100"
        help
 	  On AT91rm9200 chips where you're using a system clock derived