MAINTAINERS: Add section for NXP i.MX clock drivers

Add a section for NXP i.MX clock drivers and list myself
as the maintainer.

Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
Link: https://lore.kernel.org/r/1610542388-12078-1-git-send-email-abel.vesa@nxp.com


Acked-by: Stephen Boyd <sboyd@kernel.org>
Acked-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>