Overridable TMC serial pins, update TMC2209 docs (#14751)

Marlin/src/pins/linux/pins_RAMPS_LINUX.h

Marlin/src/pins/ramps/pins_RAMPS.h

Marlin/src/pins/ramps/pins_Z_BOLT_X_SERIES.h

config/default/Configuration_adv.h

config/examples/3DFabXYZ/Migbot/Configuration_adv.h

config/examples/AlephObjects/TAZ4/Configuration_adv.h

config/examples/Alfawise/U20/Configuration_adv.h

config/examples/AliExpress/UM2pExt/Configuration_adv.h

config/examples/Anet/A2/Configuration_adv.h

config/examples/Anet/A2plus/Configuration_adv.h

config/examples/Anet/A6/Configuration_adv.h

config/examples/Anet/A8/Configuration_adv.h

config/examples/Anet/A8plus/Configuration_adv.h

config/examples/Anet/E16/Configuration_adv.h

config/examples/AnyCubic/i3/Configuration_adv.h

config/examples/ArmEd/Configuration_adv.h

config/examples/BIBO/TouchX/cyclops/Configuration_adv.h

config/examples/BIBO/TouchX/default/Configuration_adv.h

config/examples/BQ/Hephestos/Configuration_adv.h

config/examples/BQ/Hephestos_2/Configuration_adv.h