Code sanitizations to eleminate compiler warnings & bugfix isVSBUSPlug() & bugfix Force DCDC3open & added TSpin control

[cyberman54]

@lewisxhe

I. bug fixes

• bug fixed: isVBUSPlug() always returned a wrong value
• bug fixed: FORCED_OPEN_DCDC3 always did force DCDC1 (on AXP192) or EXTEN (on AXP202), never DCDC3

II. Code sanitizations:

• strictly use of _getRegistResult
• strictly use of return <value> in non void functions
• eliminated ununsed variables to suppress compiler warnings
• removed unused an undocumented (invalid?) registers 0x50/0x51

III. Enhancements:

• added TS pin functions for battery temperature monitoring

[cyberman54]

@lewisxhe ping - could you please check, thx!

[lewisxhe]

Your submission made me see my mistake, thank you.