spl: Allow performing BSS init early before board_init_f()

On some platform we have sufficient memory available early on to allow
setting up and using a basic BSS prior to entering board_init_f(). Doing
so can for example be used to carry state over to board_init_r() without
having to resort to extending U-Boot's global data structure.

To support such scenarios add a Kconfig option called CONFIG_SPL_EARLY_BSS
to allow moving the initialization of BSS prior to entering board_init_f(),
if enabled. Note that using this option usually should go along with using
CONFIG_SPL_SEPARATE_BSS and configuring BSS to be located in memory
actually available prior to board_init_f().

Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
diff --git a/common/spl/Kconfig b/common/spl/Kconfig
index 7122c06..5978fb2 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -248,6 +248,16 @@
 	  info. Disabling this option could be useful to reduce SPL boot time
 	  (e.g. approx. 6 ms faster, when output on i.MX6 with 115200 baud).
 
+config SPL_EARLY_BSS
+	depends on ARM && !ARM64
+	bool "Allows initializing BSS early before entering board_init_f"
+	help
+	  On some platform we have sufficient memory available early on to
+	  allow setting up and using a basic BSS prior to entering
+	  board_init_f. Activating this option will also de-activate the
+	  clearing of BSS during the SPL relocation process, thus allowing
+	  to carry state from board_init_f to board_init_r by way of BSS.
+
 config SPL_DISPLAY_PRINT
 	bool "Display a board-specific message in SPL"
 	help