Blackfin arch: redo our linker script a bit

 - we can start taking advantages of defines in asm-generic/vmlinux.lds.h
 - move our L1 relocated sections into init so it gets freed after relocation

Signed-off-by: Mike Frysinger <michael.frysinger@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>