ARM: keystone: remove redundant smp_init_cpus definition

arm_dt_init_cpu_maps is called before smp_init_cpus. It makes the
platform/SoC definition of smp_init_cpus unnecessary.

Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>