imx7: Update CONFIG_SPL_STACK defaults in Kconfig

Update the Kconfig entry to have the correct defaults for i.MX7
platforms, and move the existing large comment from imx7_spl.h to
doc/imx/common/imx7.txt so that it's not lost.

Signed-off-by: Tom Rini <trini@konsulko.com>
11 files changed