Revert "common/memsize.c: Simplify RAM size detection"

This commit breaks bootup on sunxi boards, the get stuck
when running the main u-boot binary at:

CPU:   Allwinner H3 (SUN8I)
I2C:   ready
DRAM:

This reverts commit 8e7cba04.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>