MAINTAINERS: add topgit for T:

At least one tree:

	ARM/EZX SMARTPHONES (A780, A910, A1200, E680, ROKR E2 and ROKR E6)

is available via topgit.  Add mention of topgit in the MAINTAINERS
description section.

Signed-off-by: Harry Wei <harryxiyou@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>