ddr: altera: Stratix10: Use phys_size_t for memory size

Replace with phys_size_t for all memory size variables declaration
for the sake of scalability. phys_size_t is defined in
/arch/arm/include/asm/types.h.

Signed-off-by: Tien Fong Chee <tien.fong.chee@intel.com>