spl: Kconfig: Add SPL dependency to CONFIG_HANDOFF

CONFIG_HANDOFF is used in u-boot proper to locate handoff info from SPL
during pre-relocation init (in setup_spl_handoff). Add explicit dependency
on CONFIG_SPL, to fix the following build error when CONFIG_HANDOFF &&
!CONFIG_SPL:

common/board_f.c: In function ‘setup_spl_handoff’:
common/board_f.c:283:4: error: ‘gd_t {aka struct global_data}’
has no member named ‘spl_handoff’
  gd->spl_handoff = bloblist_find(BLOBLISTT_SPL_HANDOFF,
    ^~
Signed-off-by: NOvidiu Panait <ovidiu.panait@windriver.com>
Reviewed-by: NSimon Glass <sjg@chromium.org>

common/spl/Kconfig

@@ -126,7 +126,7 @@ endmenu
 
 config HANDOFF
 	bool "Pass hand-off information from SPL to U-Boot proper"
-	depends on BLOBLIST
+	depends on SPL && BLOBLIST
 	help
 	  It is useful to be able to pass information from SPL to U-Boot
 	  proper to preserve state that is known in SPL and is needed in U-Boot.