build: split CONFIG_SPL_TEXT_BASE into two different macros

We are about to move CONFIG_SPL_TEXT_BASE from header files to defconfig.
But we cannot move them as they are.

The problem is that #ifdef statements are used in board headers with
TPL support. Like this:

  #ifdef CONFIG_TPL_BUILD
  #define CONFIG_SPL_TEXT_BASE    0xD0001000
  #elif defined(CONFIG_SPL_BUILD)
  #define CONFIG_SPL_TEXT_BASE    0xff800000
  #endif

We cannot describe conditinal statments in defconfig.
One possible solution is to add CONFIG_TPL_TEXT_BASE.

This commit modifies the code as follow:

  #ifdef CONFIG_TPL_BUILD
  #define CONFIG_TPL_TEXT_BASE    0xD0001000
  #elif defined(CONFIG_SPL_BUILD)
  #define CONFIG_SPL_TEXT_BASE    0xff800000
  #endif

(include/config_fallbakcs.h should also be tweaked because some other
parts still reference to CONFIG_SPL_TEXT_BASE)

In the next commit, it will be converted into defconfig like this:

  CONFIG_SPL_TEXT_BASE=0xff800000
  CONFIG_TPL_TEXT_BASE=0xd0001000
kconfig: move CONFIG_{SPL,TPL}_TEXT_BASE to Kconfig

This commit was automatically generated by a conversion tool.
remove CONFIG_{SPL,TPL}_TEXT_BASE from config headers