Standardize Marlin SPI (part 1) (#19989)

Marlin/src/HAL/LPC1768/MarlinSPI.h

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+/**
+ * Marlin 3D Printer Firmware
+ * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
+ *
+ * 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 <https://www.gnu.org/licenses/>.
+ *
+ */
+#pragma once
+
+#include <SPI.h>
+
+/**
+ * Marlin currently requires 3 SPI classes:
+ *
+ * SPIClass:
+ *  This class is normally provided by frameworks and has a semi-default interface.
+ *  This is needed because some libraries reference it globally.
+ *
+ * SPISettings:
+ *  Container for SPI configs for SPIClass. As above, libraries may reference it globally.
+ *
+ * These two classes are often provided by frameworks so we cannot extend them to add
+ * useful methods for Marlin.
+ *
+ * MarlinSPI:
+ *  Provides the default SPIClass interface plus some Marlin goodies such as a simplified
+ *  interface for SPI DMA transfer.
+ *
+ */
+
+using MarlinSPI = SPIClass;