x86/power/64: Fix page-table setup for temporary text mapping

On a system with 4-level page-tables there is no p4d, so the pud in the pgd
should be mapped. The old code before commit fb43d6cb already did that.

The change from above commit causes an invalid page-table which causes
undefined behavior. In one report it caused triple faults.

Fix it by changing the p4d back to pud.

Fixes: fb43d6cb ('x86/mm: Do not auto-massage page protections')
Reported-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michal Kubecek <mkubecek@suse.cz>
Tested-by: Borislav Petkov <bp@suse.de>
Cc: linux-pm@vger.kernel.org
Cc: rjw@rjwysocki.net
Cc: pavel@ucw.cz
Cc: hpa@zytor.com
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lkml.kernel.org/r/1524162360-26179-1-git-send-email-joro@8bytes.org