watchdog: hpwdt: Changes to handle NX secure bit in 32bit path

This patch makes use of the set_memory_x() kernel API in order
to make necessary BIOS calls to source NMIs.

This is needed for SLES11 SP2 and the latest upstream kernel as it appears
the NX Execute Disable has grown in its control.

Signed-off by: Thomas Mingarelli <thomas.mingarelli@hp.com>
Signed-off by: Wim Van Sebroeck <wim@iguana.be>
Cc: stable@kernel.org