Blackfin arch: vmlinux.lds.S, break up our .init into separate sections

Break up our .init into separate section like all other ports do and
so that we dont mix text and data (causes disassembly headaches as
pointed out by Robin)

Cc: Robin Getz <robin.getz@analog.com>
Signed-off-by: Mike Frysinger <michael.frysinger@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>