i.MX7ULP: Set A7 core frequency to 500Mhz for B0 chip

The normal target frequency for ULP A7 core is 500Mhz, but now ROM
set the core frequency to 413Mhz. So change it to 500Mhz in u-boot.

Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
3 files changed