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 <arnd@arndb.de>
Cc: Olof Johansson <olof@lixom.net>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Mike Turquette <mturquette@linaro.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Olof Johansson <olof@lixom.net>