mimxrt/hal: Allow readSampleClkSrc to be configured by a board.

Via the MICROPY_HW_FLASH_DQS flag.

Author: d3v1c3nv11

ports/mimxrt/hal/qspi_nor_flash_config.c

@@ -24,12 +24,16 @@ __attribute__((section(".boot_hdr.conf")))
 #pragma location = ".boot_hdr.conf"
 #endif
 
+#ifndef MICROPY_HW_FLASH_DQS
+#define MICROPY_HW_FLASH_DQS kFlexSPIReadSampleClk_LoopbackFromDqsPad
+#endif
+
 const flexspi_nor_config_t qspiflash_config = {
  .memConfig =
  {
  .tag = FLEXSPI_CFG_BLK_TAG,
  .version = FLEXSPI_CFG_BLK_VERSION,
- .readSampleClkSrc = kFlexSPIReadSampleClk_LoopbackFromDqsPad,
+ .readSampleClkSrc = MICROPY_HW_FLASH_DQS,
  .csHoldTime = 3u,
  .csSetupTime = 3u,
  .busyOffset = FLASH_BUSY_STATUS_OFFSET, // Status bit 0 indicates busy.