Fix #8710

* repair reverse_pass()

And make it readeble.
This was broken a long time ago.
Not competely unfunctional but far from optimal.

* Minor speedup when calling calculate_trapezoid_for_block

2 float / to 1 foat / and 2 float *

* Various style changes

* Better off mesh behaviour for UBL

* Suggested ubl.h changes

* Nozzle.cpp: replace incorrect M_2_PI (2/pi) with 2.0 * M_PI

* Use RADIANS(360) instead of 2 * M_PI

Removed missing include file

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

* 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

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.

1) add explanations as to why software SPIs are selected

2) remove unused flag/option

still trying to fix file name

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

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-Remove outdated 256 size limitation from comments on RX_BUFFER_SIZE defines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