arm: socfpga: Add distro boot to socfpga common header

This adds a common environment and support for distro boot
in the common socfpga header.

Signed-off-by: Dalon Westergreen <dwesterg@gmail.com>
Acked-by: Marek Vasut <marex@denx.de>

--
Changes in v5:
 - Per Frank, to support OpenSuse the ENV must be after the GPT
Changes in v4:
 - Move env back to being right after the MBR
Changes in v3:
 - fix spacing between asterix
 - remove verify=n as a default setting

Changes in v2:
 - Remove unneeded CONFIG_BOOTFILE and fdt_addr
 - cleanup spacing in MMC env size

common

Signed-off-by: Dalon Westergreen <dwesterg@gmail.com>