kgdb: don't needlessly skip PAGE_USER test for Fsl booke

The bypassing of this test is a leftover from 2.4 vintage
kernels, and is no longer appropriate, or even used by KGDB.
Currently KGDB uses probe_kernel_write() for all access to
memory via the KGDB core, so it can simply be deleted.

This fixes CVE-2010-1446.

CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Paul Mackerras <paulus@samba.org>
CC: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Wufei <fei.wu@windriver.com>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>