ARM: at91: drop AT91_TIMER_HZ

Drop AT91_TIMER_HZ as this can be handled using HZ_FIXED. Initial help message
was:

On AT91rm9200 chips where you're using a system clock derived
from the 32768 Hz hardware clock, this tick rate should divide
it exactly: use a power-of-two value, such as 128 or 256, to
reduce timing errors caused by rounding.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index a1d1530..8d5c4f9 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1502,7 +1502,7 @@
 	int
 	default 200 if ARCH_EBSA110 || ARCH_S3C24XX || \
 		ARCH_S5PV210 || ARCH_EXYNOS4
-	default AT91_TIMER_HZ if ARCH_AT91
+	default 128 if SOC_AT91RM9200
 	default SHMOBILE_TIMER_HZ if ARCH_SHMOBILE_LEGACY
 	default 0