Use simpler runtime cpu dection macros.

Signed-off-by: Peng Fan <van.freenix@gmail.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Bhuvanchandra DV <bhuvanchandra.dv@toradex.com>
Cc: "Benoît Thébaudeau" <benoit.thebaudeau.dev@gmail.com>