apm821xx: MBL: make mtd chip work

apm821xx: MBL: make mtd chip work

The MBL has a 512KiB Microchip SST39VF040 chip for uboot and
not much else.

Thanks to Ewald who figured out that the "jedec-probe" vs.
"jedec-flash" was the wrong binding. With this information
and the jedec-probe support enabled => the chip works.

| physmap-flash 4fff80000.nor_flash: physmap platform flash device: [mem 0x4fff80000-0x4ffffffff]
| Found: SST 39LF040
| 4fff80000.nor_flash: Found 1 x8 devices at 0x0 in 8-bit bank

Suggested-by: Ewald Comhaire <e.comhaire@gmail.com>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>