Blackfin: make sure bss len is multiple of 4 bytes

Blackfin: make sure bss len is multiple of 4 bytes

The Blackfin on-chip BootROM requires that fill operations (which is
used for the bss) be aligned to 4 bytes (base addr and total len).
Plus, the Blackfin early init asm code assumes the same thing.  So
rather than making things work for no real gain, make sure the bss
len is padded to 4 bytes in the linker script.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>