delete Kbuild "select" of long-dead SPL_DISABLE_OF_CONTROL

>From way back in 2015:

  commit dffb86e4
  Author: Masahiro Yamada <yamada.masahiro@socionext.com>
  Date:   Wed Aug 12 07:31:54 2015 +0900

    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>
Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>

arch/arm/mach-exynos/Kconfig

@@ -116,7 +116,6 @@ config TARGET_SNOW
 config TARGET_SPRING
 	bool "Spring board"
 	select OF_CONTROL
-	select SPL_DISABLE_OF_CONTROL
 	select SUPPORT_SPL
 
 config TARGET_SMDK5420
@@ -150,7 +149,6 @@ config  TARGET_ESPRESSO7420
 	select OF_CONTROL
 	select PINCTRL
 	select PINCTRL_EXYNOS7420
-	select SPL_DISABLE_OF_CONTROL
 	select SUPPORT_SPL
 
 endchoice