board: samsung: e850-96: Add dfu_alt_info

board: samsung: e850-96: Add dfu_alt_info

Add 'dfu_alt_info' environment variable which contains:
  - Linux eMMC partitions ('esp' and 'rootfs')
  - eMMC Boot Partition A layout, where all the firmware reside

It makes it possible to update the bootloader (U-Boot). All sizes in
'dfu_alt_info' are given in 512B blocks (LBA). eMMC size is 58.2 GiB.
The eMMC Boot Partition A (mmc0boot0) layout looks like this:

                 boot0 partition (4 MiB)
       0x0 +----------------------------------+
           |         fwbl1 (12 KiB)           |
      0x18 +----------------------------------+
           |         epbl (76 KiB)            |
      0xb0 +----------------------------------+
           |         bl2 (256 KiB)            |
     0x2b0 +----------------------------------+
           |         dram_train (16 KiB)      |
     0x2d0 +----------------------------------+
           |         ect_test (50 KiB)        |
     0x334 +----------------------------------+
           |         acpm_test (130 KiB)      |
     0x438 +----------------------------------+
           |         bootloader (2 MiB)       |
    0x1438 +----------------------------------+
           |         el3_mon (256 KiB)        |
    0x1638 +----------------------------------+

where U-Boot should be flashed into 'bootloader' partition. So U-Boot
binary size should be 2 MiB or less. The whole boot0 partition is 4 MiB,
but only 2.8 MiB is currently used.

With this change, the U-Boot binary can be updated on eMMC like this:

    => dfu 0 mmc 0
    $ dfu-util -D u-boot.bin -a bootloader

Looking at E850-96 booting diagram at [1,2], it's easy to see how these
binaries are being executed in the same order they are placed in
mmc0boot0 area. E.g. fwbl1 is definitely BL1 (software part of Boot
ROM). So it's obvious the ROM code just reads the binary from eMMC at
0x0 offset into RAM (SRAM?) and executes it.

All mentioned images can be found at [3], as stated in E850-96 U-Boot
documentation. 'dram_train', 'ect_test' and 'acpm_test' areas should be
ignored -- they are not flashed with real images.

[1] doc/board/samsung/e850-96.rst
[2] https://docs.u-boot.org/en/latest/board/samsung/e850-96.html
[3] https://gitlab.com/Linaro/96boards/e850-96/images/-/tree/master/images

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>