xen/riscv: add .sbss section to .bss

Sometimes variables are located in .sbss section but it won't
be mapped after MMU will be enabled.
To avoid MMU failures .sbss should be mapped

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>

xen/arch/riscv/xen.lds.S

@@ -149,7 +149,7 @@ SECTIONS
         *(.bss.percpu.read_mostly)
         . = ALIGN(SMP_CACHE_BYTES);
         __per_cpu_data_end = .;
-        *(.bss .bss.*)
+        *(.sbss .sbss.* .bss .bss.*)
         . = ALIGN(POINTER_ALIGN);
         __bss_end = .;
     } :text