Save and restore r9 register in arm ubldr.  In old gcc 4.2, r9 was a callee-
saved register, but in arm EABI it may be either callee-saved or dedicated
to some special purpose (such as a TLS pointer).  It appears clang does not
treat it as a callee-saved register (instead using it as another work
register, similar to r12).

Another important side effect of these changes is that saving an extra
register in the push/pop statements keeps the stack aligned to an 8-byte
boundary during the self_reloc() call, as it always should have been.

As stated in the PR...

Essentially the important caller-saved registers are pushed (r0, r1, r9, lr)
before the relocation call, and popped after.  Then r8/r9 are saved as usual
for the syscall trampoline, and lr is stored in r8 (now free) as a
callee-saved value before calling into `main`.

The call to `main` can no longer be a tail call because we must restore r9
especially after main returns (although since we have used r8 to hold lr we
must also restore this).

When building for arm arches, set PKTALIGN to the max cache line size
supported by the arch, to meet u-boot's requirement that I/O be done
in cache-aligned chunks.