Fixes deficiencies with the button system on the X3
The x3 has an interesting button layout.
Multiple key presses are NOT supported unless
[BUTTON_POWER] is one of the combined keys
As you can imagine this causes problems as the power button takes
precedence in the button system and initiates a shutdown if the
key is held too long
instead of BUTTON_POWER use BUTTON_PWRALT in combination with other keys
IF using as a prerequsite button then BUTTON_POWER should be used
Multiple buttons are emulated by button_read_device but there are a few
caveats to be aware of:
Button Order Matters!
different keys have different priorities, higher priority keys 'overide'
the lower priority keys
VOLUP[7] VOLDN[6] PREV[5] NEXT[4] PLAY[3] OPTION[2] HOME[1]
There will be no true release or repeat events, the user can let off the
button pressed initially and it will still continue to appear to be
pressed as long as the second key is held
Tree scrolling is PLAY+NEXT or PLAY+PREV
Change-Id: I88dfee1c70a6a99659e8227f5becacc50cc43910
c62493e98a