init: remove adb forced config and switch to mtp.

-adb is not enabled by default, for security purposes.
Let's enable MTP in that case (this will alleviate users
having to enable it manually) and leave the debugging option up
to developer settings.

-Note: the forced adb config was there to allow for adb to start
       without delay on system init, for early debugging purposes.

Conflicts:
	p4-common.mk
init: move MTP to DEFAULT_PROPERTY

-reference d2

Conflicts:
	p4-common.mk