Kconfig: Move CONFIG_BOOTCOUNT_ALTBOOTCMD to Kconfig

Kconfig: Move CONFIG_BOOTCOUNT_ALTBOOTCMD to Kconfig

Add CONFIG_BOOTCOUNT_ALTBOOTCMD so the developer is able to add
custom altbootcmd via Kconfig when they enable BOOTCOUNT. With this now
in Kconfig, we need to move it from environment files / config.h files
and in to the defconfig file.

This was done by generating u-boot-initial-env for all platforms before
the Kconfig change, to extract altbootcmd values and then again after to
compare the result.

[trini: Perform migration to defconfigs, reword commit message]
Signed-off-by: Tom Rini <trini@konsulko.com>