[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.

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-Remove outdated 256 size limitation from comments on RX_BUFFER_SIZE defines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