Fix Rock 4C Plus pin mapping and board file

[MathijsNL]

This will fix issue #656.

I tested all pins as input and output, they all work except for the not so well documented D26. The information on the wiki matches the actual layout. Radxa gpio

@RadxaYuntian do you know where we can find more info about pin# 26 (ADC IN)?

[RadxaYuntian]

Please check page 821 of RK3399 TRM about typical application of SARADC.

[wgroeneveld]

@MathijsNL Thanks for your work and investigations, I might have lost sight of a pin or two! Cheers!

[makermelissa]

Thank you to both of you @wgroeneveld and @MathijsNL for working on this.