mtd: spi-nor: mtk-quadspi: add SNOR_HWCAPS_READ to spi_nor_hwcaps mask

SNOR_HWCAPS_READ should be supported by this controller, so add this
flag to spi_nor_hwcaps mask.

Signed-off-by: Guochun Mao <guochun.mao@mediatek.com>
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Boris Brezillon <bbrezillon@kernel.org>