[FUZE+] Rockblox plugin slight keymaps update

1) slight keymaps update
Remove mapping of BUTTON_BACK reseting game to avoid pressing it
involuntary.
Direct mapping of BUTTON_POWER to go into menu.
2) manual updated
Change-Id: I28875104c4a4058216532b9aa12bb2defabcca6d
Reviewed-on: http://gerrit.rockbox.org/352
Reviewed-by: Amaury Pouly <amaury.pouly@gmail.com>
2 files changed