ARMv7: at91: enable ICache and DCache.

For at91 armv7 SoC (SAMA5D3x), only LCD and macb used DMA.
Now as the lcd and macb driver already support dcache. So we can
enable dcache now.

Also we can enable icache without any problem.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>