fastboot: integrate block flashing back-end

fastboot: integrate block flashing back-end

1. Get partition info/size
2. Erase partition
3. Flash partition
4. BCB

Make FASTBOOT_FLASH also depend on BLK, but make sure
it doesn't affect SUNXI and ROCKCHIP platforms since they
default to y already.

Make it only default on SUNXI when MMC or NAND is enabled,
so it doesn't break the CHIP & Nintendo boards, and for ROCKCHIP
when MMC is enabled.

Signed-off-by: Dmitrii Merkurev <dimorinny@google.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
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-v7-3-9589d902fc91@linaro.org
Signed-off-by: Mattijs Korpershoek <mkorpershoek@kernel.org>