ARM: 7122/1: localtimer: add header linux/errno.h explicitly

Per the text in  Documentation/SubmitChecklist as below, we should
explicitly have header linux/errno.h in localtimer.h for ENXIO
reference.

1: If you use a facility then #include the file that defines/declares
   that facility.  Don't depend on other header files pulling in ones
   that you use.

Otherwise, we may run into some compiling error like the following one,
if any file includes localtimer.h without CONFIG_LOCAL_TIMERS defined.

  arch/arm/include/asm/localtimer.h: In function ‘local_timer_setup’:
  arch/arm/include/asm/localtimer.h:53:10: error: ‘ENXIO’ undeclared (first use in this function)

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
ARM: 7124/1: smp: Add a localtimer handler callable from C code

In order to be able to handle localtimer directly from C code instead of
assembly code, introduce handle_local_timer(), which is modeled after
handle_IRQ().

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>