power: charger: Add snapshot of qpnp-linear-charger

Initial snapshot of qpnp-linear-charger driver is taken from msm-3.18
kernel version @ commit f8b6819d0432d6 ("msm: ipa: Fix to handle
NULL pointer dereference")

Change spmi driver framework to platform driver. Add support to access
spmi registers via register mapping. Also add USB power supply and
extcon support to notify usb insertion/removal.

Change-Id: I8a6ee04540b99c5abd958a7bcbc77c3e7da4d2e5
Signed-off-by: Arulpandiyan Vadivel <avadiv@codeaurora.org>
Signed-off-by: Sundara Vinayagam <sundvi@codeaurora.org>