imx8 som: Double environment size

Closes #5

See merge request Librem5/uboot-imx!9

Create librem5 board

See merge request Librem5/uboot-imx!7

This commit creates a new board for the Purism Librem5 devkit.

- The board code was copied from the emcraft/imx8m_som board, minus the
parts which were not relevant (other DDR configs).
- The Emcraft-specific preprocessor defines have been removed.
- A new librem5.h configuration file was created.

The Emcraft-specific config options should not appear if no Emcraft
board is selected.

Enable distro boot

See merge request Librem5/uboot-imx!5

This enables distro_bootcmd for the imx8m SOM and the Librem5 dev kit.
It allows flash-kernel to work.

Load the M4 code from the same eMMC partition the SPL booted from

See merge request !4

For eMMC booting from one of their hardware boot partitions, load the M4
binary from the hwpartition the SPL booted from.

This enables booting U-boot entirely from the eMMC boot1 or boot2
hwpartitions, thus keeping the bootloader and all the SoC-specific boot
black magic out of the way of the user.

- Put the MMC device initialization part in a separate function.
- Flatten indented code by using "return" in the exception path, since
  there is no error handling to perform.
- Include the full function definition for ddr_load_train_code() in the
  preprocessor conditional, so you don't have to scroll up to see the
  function prototype for the #else case.

Use partition with bootable flag as mmcpart

See merge request Librem5/uboot-imx!3

imx8m_som.h : make the kernel verbose rather than quiet

See merge request Librem5/uboot-imx!1

Signed-off-by: Daniel Abrecht <public@danielabrecht.ch>

As the SDP protocol use the predefined ep num for communication, we can't
change its name hence reset its ep num while do ep autoconfig, this is
only apply for SPL.
Signed-off-by: Li Jun <jun.li@nxp.com>