NOR: add read() callback to struct flash_driver

Final target is to force bus_width size during CFI flash
read.
In this first step I need to replace default flash read
with flash specific implementation.
This patch introduces:
- flash_driver_read() layer;
- default_flash_read(), backward compatible;
- read() callback in struct flash_driver;
- proper initialization in every flash_driver instance.

Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>

src/flash/nor/cfi.c

@@ -2467,6 +2467,8 @@ struct flash_driver cfi_flash = {
 	.erase = cfi_erase,
 	.protect = cfi_protect,
 	.write = cfi_write,
+	/* FIXME: access flash at bus_width size */
+	.read = default_flash_read,
 	.probe = cfi_probe,
 	.auto_probe = cfi_auto_probe,
 	/* FIXME: access flash at bus_width size */