GCC4.6: Squash GTREADREG related errors

interrupts.c: In function 'interrupt_init_cpu':
interrupts.c:37: warning: implicit declaration of function 'GTREGREAD'
interrupts.c:37: error: 'LOW_INTERRUPT_CAUSE_REGISTER' undeclared (first use in
this function)
interrupts.c:37: error: (Each undeclared identifier is reported only once
interrupts.c:37: error: for each function it appears in.)
interrupts.c:37: error: 'HIGH_INTERRUPT_CAUSE_REGISTER' undeclared (first use in
this function)
interrupts.c:40: error: 'ETHERNET0_INTERRUPT_CAUSE_REGISTER' undeclared (first
use in this function)
interrupts.c:40: error: 'ETHERNET1_INTERRUPT_CAUSE_REGISTER' undeclared (first
use in this function)
interrupts.c:40: error: 'ETHERNET2_INTERRUPT_CAUSE_REGISTER' undeclared (first
use in this function)
interrupts.c:44: error: 'ETHERNET0_INTERRUPT_MASK_REGISTER' undeclared (first
use in this function)
interrupts.c:44: error: 'ETHERNET1_INTERRUPT_MASK_REGISTER' undeclared (first
use in this function)
interrupts.c:44: error: 'ETHERNET2_INTERRUPT_MASK_REGISTER' undeclared (first
use in this function)

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Mike Frysinger <vapier@gentoo.org>