add block storage emulation for NVM XIP flash devices
Some paltforms such as Corstone-1000 need to see NVM XIP raw flash
as a block storage device with read only capability.
Here NVM flash devices are devices with addressable
memory (e.g: QSPI NOR flash).
The implementation is generic and can be used by different platforms.
Two drivers are provided as follows.
nvmxip-blk :
a generic block driver allowing to read from the XIP flash
nvmxip Uclass driver :
When a device is described in the DT and associated with
UCLASS_NVMXIP, the Uclass creates a block device and binds it with
the nvmxip-blk.
Platforms can use multiple NVM XIP devices at the same time by defining a
DT node for each one of them.
Signed-off-by: Abdellatif El Khlifi <abdellatif.elkhlifi@arm.com>
