soc/mediatek/mt8192: Add SPI flash controller dual read function

Support SPI flash dual read funciton which change spi mode (1-1-1)
to dual mode (1-1-2).

Signed-off-by: CK Hu <ck.hu@mediatek.com>
Change-Id: Iabd3668fc4bc42137b7743144fc1cced4fe72737
Reviewed-on: https://review.coreboot.org/c/coreboot/+/44852
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/mediatek/mt8192/flash_controller.c

@@ -132,6 +132,9 @@ static int nor_read(const struct spi_flash *flash, u32 addr, size_t len,
 	u32 done, read_len, copy_len;
 	uint8_t *dest = (uint8_t *)buf;
 
+	setbits8(&mt8192_nor->read_dual, SFLASH_READ_DUAL_EN);
+	write8(&mt8192_nor->prgdata[3], SFLASH_1_1_2_READ);
+
 	/* DMA: start [ skip | len | drop ] = total end */
 	for (done = 0; done < total; dest += copy_len) {
 		read_len = MIN(dma_buf_len, total - done);

src/soc/mediatek/mt8192/include/soc/flash_controller.h

@@ -29,7 +29,10 @@ enum {
 	/* DMA commands */
 	SFLASH_DMA_TRIGGER	  = 1 << 0,
 	SFLASH_DMA_SW_RESET	  = 1 << 1,
-	SFLASH_DMA_WDLE_EN	  = 1 << 2
+	SFLASH_DMA_WDLE_EN	  = 1 << 2,
+	/* Dual mode */
+	SFLASH_READ_DUAL_EN	  = 0x1,
+	SFLASH_1_1_2_READ	  = 0x3b
 };
 
 /* register Offset */