microblaze: Fix paging init-zone initialization

This patch fix problem with bad zone initialization.
This bug wasn't perform because Microblaze doesn't
define CONFIG_ZONE_DMA and ZONE_NORMAL was 0 for this case
that's why free_area_init works with correct values.

Original message:
I believe that the switch from ZONE_DMA (== 0) to ZONE_NORMAL
broke the free area initialization.

Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
Signed-off-by: Michal Simek <monstr@monstr.eu>