fastboot: blk: introduce fastboot block flashing support

fastboot: blk: introduce fastboot block flashing support

Introduce fastboot block flashing functions and helpers
to be shared with the MMC implementation.

The write logic comes from the mmc implementation, while
the partition lookup is much simpler and could be extended.

For the erase logic, allmost no block drivers exposes the
erase operation, except mmc & virtio, so in order to allow
erasiong any partition a soft-erase logic has been added
to write zero-ed buffers in a loop.

Signed-off-by: Dmitrii Merkurev <dimorinny@google.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>
Tested-by: Mattijs Korpershoek <mkorpershoek@kernel.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20251121-topic-fastboot-blk-v7-1-9589d902fc91@linaro.org
Signed-off-by: Mattijs Korpershoek <mkorpershoek@kernel.org>