Revert "sh: Ensure fixmap and store queue space can co-exist."

This reverts commit 20e7c297efeca0861adcca073a0d283da659834b.
With store queues enabled the area above P4SEG has special properties
from the MMU's point of view, which was causing fixmap failure. We'll
have to do something else to satisfy the vmalloc range check.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>