ARM: at91: define CLOCK_TICK_RATE to bogus value except A91X40

We have a clocksource which renders CLOCK_TICK_RATE useless. Define
it to a bogus value to get rid of some ifdeffery.

use local LATCH for at91rm9200 timer

but keep it for A91X40 as we do not use a clocksource

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>