mxssb: Properly implement BOOTABLE section flag

The BOOTABLE flag was set by default during development. This is
not correct, implement a proper BOOTABLE flag for each section and
make this configurable from the command file.
Signed-off-by: Marek Vasut <marex@denx.de>

mxsimage.mx23.cfg

-SECTION 0x0
+SECTION 0x0 BOOTABLE
  TAG LAST
  LOAD     0x0        spl/u-boot-spl.bin
  CALL     0x14       0x0

mxsimage.mx28.cfg

-SECTION 0x0
+SECTION 0x0 BOOTABLE
  TAG LAST
  LOAD     0x0        spl/u-boot-spl.bin
  LOAD IVT 0x8000     0x14

mxssb.c

@@ -685,6 +685,7 @@ static int sb_parse_sections(struct sb_image_ctx *ictx)
 	struct sb_section_ctx *sctx, *head = NULL, *prev = NULL;
 	struct sb_sections_header *shdr;
 	int ret;
+	uint32_t bootable = 0;
 	long id;
 	char *tok, *line;
 
@@ -709,6 +710,11 @@ static int sb_parse_sections(struct sb_image_ctx *ictx)
 		if (id < 0)
 			goto fail;
 
+		bootable = 0;
+		tok = strtok(NULL, " ");
+		if (tok && (strlen(tok) == 8) && !strncmp(tok, "BOOTABLE", 8))
+			bootable = SB_SECTION_FLAG_BOOTABLE;
+
 		sctx = calloc(1, sizeof(*sctx));
 		if (!sctx)
 			goto fail;
@@ -727,12 +733,11 @@ static int sb_parse_sections(struct sb_image_ctx *ictx)
 			goto fail;
 
 		shdr = &sctx->payload;
-		/* FIXME -- bootable by default. */
-		sctx->boot = 1;
 
+		sctx->boot = bootable;
 		shdr->section_number = id;
 		shdr->section_size = sctx->size / SB_BLOCK_SIZE;
-		shdr->section_flags = sctx->boot ? SB_SECTION_FLAG_BOOTABLE : 0;
+		shdr->section_flags = bootable;
 
 		ictx->section_count++;