ARM: keystone2: Enable CONFIG_DISPLAY_CPUINFO

Add print_cpuinfo() function and enable
CONFIG_DISPLAY_CPUINFO for keystone platforms,
so that cpu info can be displayed during boot.

Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Vitaly Andrianov <vitalya@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>