STM32F103.. reorganization, SKR mini fix (#15398)

.circleci/config.yml

.travis.yml

Marlin/src/core/boards.h

Marlin/src/inc/SanityCheck.h

Marlin/src/pins/pins.h

Marlin/src/pins/stm32/pins_BIGTREE_SKR_E3_DIP.h

Marlin/src/pins/stm32/pins_BIGTREE_SKR_MINI_E3.h

Marlin/src/pins/stm32/pins_BIGTREE_SKR_MINI_V1_1.h

buildroot/share/PlatformIO/ldscripts/STM32F103RC_SKR_MINI.ld

buildroot/share/PlatformIO/ldscripts/STM32F103VE_longer.ld

buildroot/share/PlatformIO/scripts/STM32F103RC_SKR_MINI.py

buildroot/share/PlatformIO/scripts/STM32F103RC_fysetc.py

buildroot/share/PlatformIO/scripts/STM32F103VE_longer.py

buildroot/share/git/mftest

buildroot/share/tests/STM32F103CB_malyan-tests

buildroot/share/tests/STM32F103RC_bigtree-tests

buildroot/share/tests/STM32F103RC_bigtree_USB-tests

buildroot/share/tests/STM32F103RC_fysetc-tests

buildroot/share/tests/STM32F103RE-tests

buildroot/share/tests/STM32F103VE_longer-tests