arm, at91: add icache support

add at least icache support for at91 based boards.
This speeds up NOR flash access on an at91sam9g15
based board from 15.2 seconds reading 8 MiB from
a SPI NOR flash to 5.7 seconds.

Signed-off-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Andreas Bießmann <andreas@biessmann.org>
diff --git a/arch/arm/mach-at91/arm926ejs/Makefile b/arch/arm/mach-at91/arm926ejs/Makefile
index ddc323f..d36e15a 100644
--- a/arch/arm/mach-at91/arm926ejs/Makefile
+++ b/arch/arm/mach-at91/arm926ejs/Makefile
@@ -18,6 +18,7 @@
 obj-$(CONFIG_AT91SAM9X5)	+= at91sam9x5_devices.o
 obj-$(CONFIG_AT91_EFLASH)	+= eflash.o
 obj-$(CONFIG_AT91_LED)	+= led.o
+obj-y += cache.o
 obj-y += clock.o
 obj-y += cpu.o
 obj-y	+= reset.o