brcm63xx: enable KEXEC for SMP again

It seems it compiles again, so there is no reason to keep it disabled.

Signed-off-by: Jonas Gorski <[email protected]>

target/linux/brcm63xx/smp/config-default

@@ -1,5 +1,4 @@
 CONFIG_CPU_RMAP=y
-# CONFIG_KEXEC is not set
 CONFIG_MUTEX_SPIN_ON_OWNER=y
 CONFIG_NR_CPUS=2
 CONFIG_RCU_STALL_COMMON=y