ARM: dts: at91: sama5d2: use "atmel,sama5d3-nfc" compatible for nfc

An error in documentation of the NAND Flash Controller (NFC) led to choose
another compatibility string for sama5d2 with an impact on the NAND flash
ready/busy information. It was producing the error message:

atmel_nand 80000000.nand: Time out to wait for interrupt: 0x08000000

and had an impact on performance.

So, switch back to the classical "atmel,sama5d3-nfc" compatibility string for
this SoC which gives the proper ready/busy bit information. The NAND flash
driver will be updated to remove the support for this different
implementation.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Acked-by: Romain Izard <romain.izard.pro@gmail.com>
[nicolas.ferre@atmel.com: change commit message]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>