MAINTAINERS: nxp-mpu: add more collaborators

Add yangbolu1991 and Zhiqiang-Hou as the collaborators for NXP MPU,
yangbolu1991 has contributed a lot of in scope of MPU M-core and
Zhiqiang-Hou has contributed a lot of in scope of MPU A-Core, they
could help to fast the review process.

Signed-off-by: Jiafei Pan <Jiafei.Pan@nxp.com>