configs: Add support in Kconfig and convert for armada boards

Move the DEFAULT_ENV_IS_RW to Kconfig for easier configuration.
Hence, add the CONFIG_DEFAULT_ENV_IS_RW config to the defconfig files
to allow enabling them for armada boards.

Signed-off-by: Algapally Santosh Sagar <santoshsagar.algapally@amd.com>
Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Link: https://lore.kernel.org/r/20230921112043.3144726-2-venkatesh.abbarapu@amd.com


Signed-off-by: Michal Simek <michal.simek@amd.com>