all: add eraseGroupSize at partitions.yaml file

To assure small partitions can be erased by u-boot, define eraseGroupSize variable to be used by gen_partition_xml.

Depends on https://gitlab.baylibre.com/baylibre/mediatek/rita/vendor/mediatek/tools/mbr/-/merge_requests/2

Signed-off-by: Vitor Sato Eschholz vsatoes@baylibre.com