ARM: 8850/1: use memblocks_present

arm_memory_present is doing same thing as memblocks_present, so
let's use common code memblocks_present instead of platform
specific arm_memory_present.

Patchwork: https://patchwork.kernel.org/patch/10805693/

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>