of: flip CONFIG_SPL_DISABLE_OF_CONTROL into CONFIG_SPL_OF_CONTROL

As we discussed a couple of times, negative CONFIG options make our
life difficult; CONFIG_SYS_NO_FLASH, CONFIG_SYS_DCACHE_OFF, ...
and here is another one.

Now, there are three boards enabling OF_CONTROL on SPL:
 - socfpga_arria5_defconfig
 - socfpga_cyclone5_defconfig
 - socfpga_socrates_defconfig

This commit adds CONFIG_SPL_OF_CONTROL for them and deletes
CONFIG_SPL_DISABLE_OF_CONTROL from the other boards to invert
the logic.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>