arm: socfpga: Move cache_enable to CPU code

Move icache_enable() and dcache_enable() function calls from
board code into the CPU code and into the enable_caches()
function. This is how the cache enabling code was designed
to work.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Dinh Nguyen <dinguyen@altera.com>
Cc: Pavel Machek <pavel@denx.de>
Cc: Marek Vasut <marex@denx.de>
Cc: Tom Rini <trini@ti.com>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Wolfgang Denk <wd@denx.de>
Acked-by: Pavel Machek <pavel@denx.de>