[SPARC64]: Mark most of initial bootup asm as .text.init.ref_ok

We can't mark the whole thing init because there are dependencies
in bootloaders that assume that _start, or whatever the image
entry value, is 2 instructions before the "HdrS" signature.

In fact, TILO assumes this entry is always at 0x4000, yikes!

Also, right after the bootloader info area there are OBP strings and
values that get used later in the boot process, and those are not all
provably .init yet.

Signed-off-by: David S. Miller <davem@davemloft.net>