riscv: Include bss subsections in linker script

When we build with -fdata-sections we may end up with bss subsections. Our
linker script explicitly lists only a single consecutive bss section though.

Adapt the statement to also include subsections.

Signed-off-by: Alexander Graf <agraf@suse.de>

arch/riscv/cpu/ax25/u-boot.lds

@@ -82,7 +82,7 @@ SECTIONS
 
 	.bss : {
         __bss_start = .;
-        *(.bss)
+        *(.bss*)
 		. = ALIGN(4);
 		__bss_end = .;
 	}