MA-15062-2 change mcu firmware partition name

MA-15062-2 change mcu firmware partition name

new imx8mn chips have Cortex-M7 inside, not like any other existing
multi-core i.MX MPU, users may manually flash mcu firmware with
fastboot, partition name need to be specified at the same time, so the
mcu firmware partition name need to be changed. related enum and
variable names are also modified.

Change-Id: Ia801e76fb3a20d0074dbbc1433258358c1a53907
Signed-off-by: faqiang.zhu <faqiang.zhu@nxp.com>
Signed-off-by: Ji Luo <ji.luo@nxp.com>
(cherry picked from commit dc25b7b27fa5c2293d09789a338a1aed2e3a010f)