[Keyboard] Use old custom matrix for Drop Planck+Preonic (#14488)

Co-authored-by: Ryan <fauxpark@gmail.com>
Co-authored-by: Jack Humbert <jack.humb@gmail.com>

keyboards/planck/rev6_drop/mcuconf.h

@@ -0,0 +1,39 @@
+/* Copyright 2020 QMK Contributors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include_next "mcuconf.h"
+
+// The SysTick timer from the normal quantum/stm32 uses TIM2 -- the WS2812 pin used
+// on the Planck requires the use of TIM2 to run PWM -- rework which timers are
+// allocated for PWM usage.
+#undef STM32_PWM_USE_TIM2
+#define STM32_PWM_USE_TIM2 TRUE
+
+#undef STM32_DAC_USE_DAC1_CH1
+#define STM32_DAC_USE_DAC1_CH1 TRUE
+#undef STM32_DAC_USE_DAC1_CH2
+#define STM32_DAC_USE_DAC1_CH2 TRUE
+#undef STM32_GPT_USE_TIM6
+#define STM32_GPT_USE_TIM6 TRUE
+#undef STM32_GPT_USE_TIM7
+#define STM32_GPT_USE_TIM7 TRUE
+#undef STM32_GPT_USE_TIM8
+#define STM32_GPT_USE_TIM8 TRUE
+
+// As mentioned above, we need to reallocate the SysTick timer used from
+// TIM2 to TIM3.
+#undef STM32_ST_USE_TIMER
+#define STM32_ST_USE_TIMER 3