battery mgmt: charging and charging state

1) now changing or not is defined by variable battery_charging
2) battery state definition included

Signed-off-by: Ajay <ajay@moxiedevices.com>
pv mgmt: pv ready for charging

is pv ready for charging? decided by pv_ready variable.

This veriable can be set and reset by different functions.

Signed-off-by: Ajay <ajay@moxiedevices.com>
main: pv mgmt: set pv ready for charing

when pv voltage is between PV_BASE_VOLT_LOW PV_BASE_VOLT_HI, it means pv
is ready for changing.
makefile: pv_mgmt added

Signed-off-by: Ajay <ajay@moxiedevices.com>