Always set the sp reg to the cfa for DWARF.

There are a few places where it is assumed that this register is
set to the cfa value when interpreting DWARF information.

Add a testcase for unwinding art_quick_osr_stub on ARM.

Bug: 73954823

Test: Ran libunwindstack/libbacktrace unit tests.
Test: Random debuggerd -b of process on a hikey.
Test: Ran the 137 art test on host.
Change-Id: Ida6ccdc38c3cfeea6b57fe861a0cc127b150b790