Fix handling of PT_GNU_EH_FRAME.

The bias for the PT_GNU_EH_FRAME was using the paddr instead of vaddr.
This doesn't match the way the load bias is calculated, which always
use vaddr - offset, so change to use vaddr.

Found on an old x86 device that has a vdso that sets vaddr differently
from paddr.

Add a new offline test to catch this case and update the elf interface
unit tests.

Also, fix a small bug in the unwind_for_offline tool.

Bug: 142365899

Test: Unit tests pass.
Change-Id: I5f0bf062dd8ee45aa8553189ba493ec962e0b059