board_r: Support calling the main program after ulib init

For boards where ulib starts first we need to jump to the main program
afterwards. Add the logic for this.

Drop the noreturn attribute from board_init_r() and board_init_f_r to
avoid needing #ifdef in the C file.

Signed-off-by: Simon Glass <simon.glass@canonical.com>

arch/x86/include/asm/u-boot-x86.h

@@ -129,7 +129,7 @@ void __noreturn board_init_f_r_trampoline(ulong sp);
  * This is used to jump from pre-relocation to post-relocation U-Boot. It
  * enables the cache and jump to the new location.
  */
-void __noreturn board_init_f_r(void);
+void board_init_f_r(void);
 
 /*
  * board_init_f_r_trampoline64() - jump to relocated address with new stack