riscv: make sure the cores stay looping in .Lsecondary_park

The code in secondary_park is currently placed in the .init section. The
kernel reclaims and clears this code when it finishes booting. That
causes the cores parked in it to go to somewhere unpredictable, so we
move this function out of init to make sure the cores stay looping there.

The instruction bgeu a0, t0, .Lsecondary_park may have "a relocation
truncated to fit" issue during linking time. It is because that sections
are too far to jump. Let's use tail to jump to the .Lsecondary_park.

Signed-off-by: Greentime Hu <greentime.hu@sifive.com>
Reviewed-by: Anup Patel <anup.patel@sifive.com>
Cc: Andreas Schwab <schwab@suse.de>
Cc: stable@vger.kernel.org
Fixes: 76d2a049 ("RISC-V: Init and Halt Code")
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>