Tentative Teensy 3.5 support (#14420)

* Tentative Teensy 3.5 support

* Set firmware format to .hex for ARM Teensys

* Got to "device descriptor failed" by comparing with Teensy 3.6 code

* Drop down to 96MHz...

* Bump back up to 120MHz

keyboards/handwired/onekey/teensy_35/mcuconf.h

@@ -0,0 +1,50 @@
+/*
+    ChibiOS - Copyright (C) 2006..2015 Giovanni Di Sirio
+
+    Licensed under the Apache License, Version 2.0 (the "License");
+    you may not use this file except in compliance with the License.
+    You may obtain a copy of the License at
+
+        http://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing, software
+    distributed under the License is distributed on an "AS IS" BASIS,
+    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+    See the License for the specific language governing permissions and
+    limitations under the License.
+*/
+
+#ifndef _MCUCONF_H_
+#define _MCUCONF_H_
+
+#define K60x_MCUCONF
+
+/*
+ * HAL driver system settings.
+ */
+
+/* Select the MCU clocking mode below by enabling the appropriate block. */
+
+/* PEE mode - 120MHz system clock driven by external crystal. */
+#define KINETIS_MCG_MODE            KINETIS_MCG_MODE_PEE
+#define KINETIS_PLLCLK_FREQUENCY    120000000UL  // 120 MHz (RUN)
+#define KINETIS_SYSCLK_FREQUENCY    KINETIS_PLLCLK_FREQUENCY
+#define KINETIS_BUSCLK_FREQUENCY    60000000UL
+#define KINETIS_FLASHCLK_FREQUENCY  24000000UL  // 24 MHz (RUN)
+
+#define KINETIS_CLKDIV1_OUTDIV1 1  // -> 0
+#define KINETIS_CLKDIV1_OUTDIV2 2  // -> 1
+#define KINETIS_CLKDIV1_OUTDIV4 5  // -> 4
+
+/*
+ * SERIAL driver system settings.
+ */
+#define KINETIS_SERIAL_USE_UART0              TRUE
+
+/*
+ * USB driver settings
+ */
+#define KINETIS_USB_USE_USB0                  TRUE
+#define KINETIS_USB_USB0_IRQ_PRIORITY         5
+
+#endif /* _MCUCONF_H_ */