MAINTAINERS: Add few more Keystone drivers

MAINTAINERS: Add few more Keystone drivers

Update MAINTAINERS file for recently added reset controller, AEMIF
and clocksource driver for Keystone SOCs.

The EMIF memory controller driver is also added along with AEMIF.

Cc: Arnd Bergmann <[email protected]>
Cc: Olof Johansson <[email protected]>
Cc: Kevin Hilman <[email protected]>
Cc: Mike Turquette <[email protected]>
Cc: Daniel Lezcano <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Santosh Shilimkar <[email protected]>
Signed-off-by: Olof Johansson <[email protected]>