parisc: Additionally check for in_atomic() in page fault handler

Craig Estey noticed that we didn't checked for in_atomic() in our page fault
handler like other architectures. This commit adds this check by using
faulthandler_disabled() which includes a check for pagefault_disabled() and
in_atomic().

Reported-by: Craig Estey <cae370@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>