m25p80: Add basic support for the SFDP command

m25p80: Add basic support for the SFDP command

JEDEC STANDARD JESD216 for Serial Flash Discovery Parameters (SFDP)
provides a mean to describe the features of a serial flash device
using a set of internal parameter tables.

This is the initial framework for the RDSFDP command giving access to
a private SFDP area under the flash. This area now needs to be
populated with the flash device characteristics, using a new
'sfdp_read' handler under FlashPartInfo.

Reviewed-by: Francisco Iglesias <frasse.iglesias@gmail.com>
Message-Id: <20220722063602.128144-2-clg@kaod.org>
Message-Id: <20221013161241.2805140-2-clg@kaod.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>