Add plugin support for wilco-ec battery care

[braveheartleo]

Modified 65-dell to add plugin support for wilco-ec battery care on a Dell laptop that is using Wilco EC.

This is for the feature requested at #838. Sample output follows.

# tlp-stat -b -v
--- TLP 1.9.0 --------------------------------------------

+++ Battery Care
Plugin: wilco-ec
Supported features: charge thresholds
Driver usage:
* natacpi (wilco_charger) = active (charge thresholds)
Parameter value ranges:
* START_CHARGE_THRESH_BAT0/1:  50..95(default)
* STOP_CHARGE_THRESH_BAT0/1:   55..100(default)

/sys/class/power_supply/wilco-charger/charge_control_start_threshold = 55 [%]
/sys/class/power_supply/wilco-charger/charge_control_end_threshold = 60 [%]
/sys/class/power_supply/wilco-charger/charge_type           = Custom

+++ Battery Status: BAT0
/sys/class/power_supply/BAT0/manufacturer                   = SMP-ATL3.61
/sys/class/power_supply/BAT0/model_name                     = DELL 7VTMN8C
/sys/class/power_supply/BAT0/cycle_count                    =     15
/sys/class/power_supply/BAT0/charge_full_design             =   4500 [mAh]
/sys/class/power_supply/BAT0/charge_full                    =   4500 [mAh]
/sys/class/power_supply/BAT0/charge_now                     =   2678 [mAh]
/sys/class/power_supply/BAT0/current_now                    =      1 [mA]
/sys/class/power_supply/BAT0/status                         = Not charging

/sys/class/power_supply/BAT0/voltage_min_design             =  11400 [mV]
/sys/class/power_supply/BAT0/voltage_now                    =  11612 [mV]

Charge                                                      =   59.5 [%]
Capacity                                                    =  100.0 [%]

[linrunner]

Thank you. I've merged locally, squashed your two commits and pushed to https://github.com/linrunner/TLP/tree/bat.d/wilco-ec

Let's continue with testing in the original issue -> #838

BTW: Please restrain from posting diffs in a PR message. Just takes up space and causes confusion. The Github WebUI does this itself and better.