msm_otg: hack to allow externally powered usb host mode

Force ID_A (host mode + charging) on detection of proprietary charger (Apple-compatible charger with voltage on D+/D-).
Unforce ID_A on PMIC: BSV clear (detection of loss of charger).
Simulate ACA since using ID_A for host mode (prevents host from getting stuck in suspended state).
Two test cases for detection of actual proprietary charger (extra debug output for now).
Remove charge current limit in host mode (ID_A).
Enable debugfs /sys/kernel/debug/msm_otg/mode for manual otg mode manipulation.
Always force requested mode (debugfs).

Note: ID pin detection not working (perhaps due to Slimport), hence the "alternate" triggers used to switch to/from host mode.