arm: Support pre-relocation malloc()

Add support for re-relocation malloc() in arm's start-up code.

Signed-off-by: Simon Glass <sjg@chromium.org>

README

@@ -3752,6 +3752,9 @@ Configuration Settings:
 		Pre-relocation malloc() is only supported on sandbox
 		at present but is fairly easy to enable for other archs.
 
+		Pre-relocation malloc() is only supported on ARM at present
+		but is fairly easy to enable for other archs.
+
 - CONFIG_SYS_BOOTM_LEN:
 		Normally compressed uImages are limited to an
 		uncompressed size of 8 MBytes. If this is not enough,

arch/arm/lib/crt0.S

@@ -78,7 +78,10 @@ clr_gd:
 	strlo	r0, [r1]		/* clear 32-bit GD word */
 	addlo	r1, r1, #4		/* move to next */
 	blo	clr_gd
-
+#if defined(CONFIG_SYS_MALLOC_F_LEN) && !defined(CONFIG_SPL_BUILD)
+	sub	sp, sp, #CONFIG_SYS_MALLOC_F_LEN
+	str	sp, [r9, #GD_MALLOC_BASE]
+#endif
 	/* mov r0, #0 not needed due to above code */
 	bl	board_init_f