linker: tls: fix tdata/tbss locations

__tbss_start should be a virtual address.
__tdata_start should also be a virtual address, unless we're
using XIP in which case each thread should copy its thread-
local data out of flash.

Fixes issues with a kernel linked at a virtual address.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>