add missing files from 2.1.2 merge

fixes 67c7ce7b79

ini/samd21.ini

@@ -0,0 +1,26 @@
+#
+# Marlin Firmware
+# PlatformIO Configuration File
+#
+
+#################################
+#                               #
+#      SAMD21 Architecture      #
+#                               #
+#################################
+
+#
+# Adafruit Grand Central M4 (Atmel SAMD51P20A ARM Cortex-M4)
+#
+[env:SAMD21_minitronics20]
+platform         = atmelsam
+board            = minitronics20
+build_flags      = ${common.build_flags} -std=gnu++17
+                   -DUSBCON -DUSBD_USE_CDC -D__SAMD21__ -DARDUINO_SAMD_MINITRONICS20  -Wno-deprecated-declarations -DU8G_HAL_LINKS -DDEBUG
+                   -IMarlin/src/HAL/SAMD21/u8g
+build_unflags    = -std=gnu++11
+build_src_filter = ${common.default_src_filter} +<src/HAL/SAMD21>
+lib_deps         = ${common.lib_deps}
+extra_scripts    = ${common.extra_scripts}
+                   pre:buildroot/share/PlatformIO/scripts/SAMD21_minitronics20.py
+debug_tool       = atmel-ice