boot: Move framebuffer reservation to separate helper

Create separate helper for just reserving framebuffer region without
creating or enabling simple-framebuffer node.

This is useful for scenarios where user want to preserve the bootloader
splash screen till OS boots up and display server gets started without
displaying anything else in between and thus not requiring
simple-framebuffer.

Signed-off-by: Devarsh Thakkar <devarsht@ti.com>
Reviewed-by: Nikhil M Jain <n-jain1@ti.com>

include/fdt_support.h

@@ -423,6 +423,8 @@ int arch_fixup_memory_node(void *blob);
 int fdt_setup_simplefb_node(void *fdt, int node, u64 base_address, u32 width,
 			    u32 height, u32 stride, const char *format);
 
+int fdt_add_fb_mem_rsv(void *blob);
+
 int fdt_overlay_apply_verbose(void *fdt, void *fdto);
 
 int fdt_valid(struct fdt_header **blobp);