watchdog: hpwdt (5/12): Make x86 assembly ifdef guard more strict

The 32-bit assembly is guarded by an #ifndef CONFIG_X86_64. Kconfig prevents
us from building this driver on !X86, so that happens to suffice - but we
should really lock it down to #ifdef CONFIG_X86_32.

Signed-off-by: dann frazier <dannf@hp.com>
Acked-by: Thomas Mingarelli <Thomas.Mingarelli@hp.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>