ARM: 5728/1: Proper prefetch abort handling on ARMv6 and ARMv7

Currently, on ARMv6 and ARMv7, if an application tries to execute
code (or garbage) on non-executable page it hangs. It caused by
incorrect prefetch abort handling. Now every prefetch abort
processes as a translation fault.

To fix this we have to analyze instruction fault status register
to figure out reason why we've got the abort and process it
accordingly.

To make IFSR different from DFSR we set bit 31 which is reserved in
both IFSR and DFSR.

This patch also tries to protect from future hangs on unexpected
exceptions. An application will be killed if unexpected exception
type was received.

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>