e820_alloc_memory requires 4k alignment, so conversion to size is
encapsulated in the function. And then the pre-condition of
`size_arg` is removed.
Tracked-On: #6805
Signed-off-by: Yuanyuan Zhao <yuanyuan.zhao@linux.intel.com>
Reviewed-by: Wang, Yu1 <yu1.wang@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>