x86, nmi, drivers: Fix nmi splitup build bug

nmi.c needs an #include <linux/mca.h>:

 arch/x86/kernel/nmi.c: In function ‘unknown_nmi_error’:
 arch/x86/kernel/nmi.c:286:6: error: ‘MCA_bus’ undeclared (first use in this function)
 arch/x86/kernel/nmi.c:286:6: note: each undeclared identifier is reported only once for each function it appears in

Another one is the hpwdt driver:

 drivers/watchdog/hpwdt.c:507:9: error: ‘NMI_DONE’ undeclared (first use in this function)

Signed-off-by: Ingo Molnar <mingo@elte.hu>