Add Arm Teensys to mcu_selection.mk (#8026)

* Add Arm Teensys to mcu_selection.mk

* Roll back halfkeyboard keymap changes

* Remove extra newline

keyboards/whitefox/rules.mk

@@ -1,15 +1,5 @@
-# project specific files
-SRC =	matrix.c \
-	led.c
-
-## chip/board settings
-# - the next two should match the directories in
-#   <chibios>/os/hal/ports/$(MCU_FAMILY)/$(MCU_SERIES)
-# - For Teensies, FAMILY = KINETIS and SERIES is either
-#   KL2x (LC) or K20x (3.0,3.1,3.2).
-# - For Infinity KB, SERIES = K20x
-MCU_FAMILY = KINETIS
-MCU_SERIES = K20x
+# MCU name
+MCU = MK20DX256
 
 # Linker script to use
 # - it should exist either in <chibios>/os/common/ports/ARMCMx/compilers/GCC/ld/
@@ -23,14 +13,6 @@ MCU_SERIES = K20x
 #   - MK20DX256BLDR8 for Infinity ErgoDox with Kiibohd bootloader
 MCU_LDSCRIPT = MK20DX256BLDR8
 
-# Startup code to use
-#  - it should exist in <chibios>/os/common/ports/ARMCMx/compilers/GCC/mk/
-# - STARTUP =
-#   - kl2x for Teensy LC
-#   - k20x5 for Teensy 3.0 and Infinity KB
-#   - k20x7 for Teensy 3.1 and 3.2
-MCU_STARTUP = k20x7
-
 # Board: it should exist either in <chibios>/os/hal/boards/
 #  or <this_dir>/boards
 # - BOARD =
@@ -40,20 +22,6 @@ MCU_STARTUP = k20x7
 #   - MCHCK_K20 for Infinity KB
 BOARD = IC_TEENSY_3_1
 
-# Cortex version
-# Teensy LC is cortex-m0; Teensy 3.x are cortex-m4
-MCU  = cortex-m4
-
-# ARM version, CORTEX-M0/M1 are 6, CORTEX-M3/M4/M7 are 7
-# I.e. 6 for Teensy LC; 7 for Teensy 3.x
-ARMV = 7
-
-# Vector table for application
-# 0x00000000-0x00001000 area is occupied by bootlaoder.*/
-# The CORTEX_VTOR... is needed only for MCHCK/Infinity KB
-#OPT_DEFS = -DCORTEX_VTOR_INIT=0x00001000
-OPT_DEFS =
-
 DFU_ARGS = -d 1c11:b007
 DFU_SUFFIX_ARGS = -p b007 -v 1c11
 
@@ -75,6 +43,10 @@ BACKLIGHT_ENABLE = yes
 BACKLIGHT_DRIVER = custom
 VISUALIZER_ENABLE = yes
 
+# project specific files
+SRC = matrix.c \
+      led.c
+
 LED_DRIVER = is31fl3731c
 LED_WIDTH = 16
 LED_HEIGHT = 5