ARM: msm: Fix early debug uart mapping on some memory configs

The uart mapping runs into the space allocated for lowmem on some
8960 boards when we have more than 512Mb of memory. We were
getting lucky before and our mapping wasn't part of DDR. Move the
mapping up into the vmalloc area which will always be outside of
the lowmem mapping regardless of how much lowmem actually exists.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: David Brown <davidb@codeaurora.org>