edminiv2: Move CONFIG_SPL_LDSCRIPT to defconfig

As there is only one machine under mach-orion5x, having a Kconfig entry
for SPL_LDSCRIPT is not helpful, move this to the defconfig file.

Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Masahiro Yamada <masahiroy@kernel.org>