arm64: zynqmp: Do not duplicate flash partition label property

arm64: zynqmp: Do not duplicate flash partition label property

In kernel 5.4, support has been added for reading MTD devices via the nvmem
API.
For this the mtd devices are registered as read-only NVMEM providers under
sysfs with the same name as the flash partition label property.

So if flash partition label property of multiple flash devices are
identical then the second mtd device fails to get registered as a NVMEM
provider.

This patch fixes the issue by having different label property for different
flashes.

Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/6c4b9b9232b93d9e316a63c086540fd5bf6b8687.1623684253.git.michal.simek@xilinx.com