Convert Altera DDR SDRAM driver to use Kconfig method.
Enable ALTERA_SDRAM by default if it is on Gen5 target.
Arria 10 will have different driver.

Signed-off-by: Tien Fong Chee <tien.fong.chee@intel.com>
Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>