When the CPU is in wait state, do not wake-up if an interrupt can't be
taken. This avoid host CPU running at 100% if a device (e.g. timer) has
an interrupt line left enabled.

Also factorize code to check if interrupts are enabled in
cpu_mips_hw_interrupts_pending().

Based on a patch from Edgar E. Iglesias <edgar.iglesias@gmail.com>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>
Acked-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>