ARM: S3C: Change VMALLOC_END to use more vmalloc()/ioremap() area

This patch changes VMALLOC_END from 0xE0000000 to 0xF6000000, because
some systems want to use more vmalloc()/ioremap() area and now don't use
from at 0xE0000000 to 0xF6000000 (the start of Samsung SoCs' VA space)

Cc: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>