sh: Define _ebss for uClinux MTD map driver.

The uClinux MTD device uses _ebss, add the symbol and corresponding
export.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/kernel/vmlinux.lds.S

@@ -107,6 +107,7 @@ SECTIONS
   	*(.bss.page_aligned)
   	*(.bss)
 	. = ALIGN(4);
+	_ebss = .;			/* uClinux MTD sucks */
 	_end = . ;
   }