[2.0.x] Cleanup, bugfixes, parity with 1.1.x

[2.0.x] Don't split first_move while homing or probing

While homing or probing it might be bad if the stop/trobe triggers during the first part and the second is still in the buffer.

Pin K7 number in fastio1280.h is 69, but it's also ADC15 pin. 
To get correct value from ADC reading it should be set as 15.

Addressing #8676

[2.0.x] Compilation errors with PIDTEMPBED only

* fix for #8669

* Update G28.cpp

Possibly more should be brought over? Discussion at #8471

Addressing https://github.com/MarlinFirmware/Marlin/pull/8575#discussion_r154536617

[2.0.x] Support for RAMPS Plus (3DYMY)

[2.0.x] SERIAL_XON_XOFF not supported on USB-native AVR devices

[2.0.x] Split first move to planner for better chaining

User could enable SERIAL_XON_XOFF on USB-native devices and it would not be enabled without warning, but M115 would report the capability as available.

[2.0.x] LPC1768 - add explanations in spi_pins.h

1) add explanations as to why software SPIs are selected

2) remove unused flag/option

[2.0.x] MKS Sbase support for RepRap Discount Full Graphic Smart Controller

still trying to fix file name

[2.0.x] Revert PR #8611 — split first planner move

This reverts commit 824980e70e, reversing
changes made to aa7efb96bf.

[2.0.x][LPC1768][FIX] NUM_DIGITAL_PINS was negative, fixes PWM, arduino io functions, M42, M43, M226, probably also Servo, some LCD, soft spi, SoftwareSerial, ... may be others

[2.0.x][LPC1768][fix] Implement GET_TIMER and other GET_xxx, fixes PWM

[2.0.x] Fix M49 so that it does not hang the terminal console

[2.0.x] Example configurations for Wanhao Duplicator 6

[2.0.x] Report SERIAL_XON_XOFF in M115

[2.0.x] Use custom segment length for UBL Cartesian

[2.0.x] Split first planner move for better chaining

Address #8573, #8595

-Report SERIAL_XON_XOFF in Extended Capabilites M115 report for hosts
-Remove outdated 256 size limitation from comments on RX_BUFFER_SIZE defines
-Update error message conditions