socfpga: Relocate arch common functions away from board

To move the arch common function away from board folder to
arch/arm/cpu/armv7/socfpga folder. Its to avoid code duplication
for other non Altera dev kit which is using socfpga device.

Signed-off-by: Chin Liang See <clsee@altera.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Detlev Zundel <dzu@denx.de>
Cc: Pavel Machek <pavel@denx.de>
Cc: Dinh Nguyen <dinguyen@altera.com>
Acked-by: Detlev Zundel <dzu@denx.de>