Revert "ARM: 7169/1: topdown mmap support"

commit 7dbaa466
(ARM: 7169/1: topdown mmap support) allocates mmap addresses from
the top addresses instead of the bottom. Unfortunately, some
userspace components are broken and do checks such as the following:

void* addr = mmap(...);
// Top bit is now the sign bit...
int test = (int)addr;
if (test < 0) {
	//failure
}

Which means that any address greater than 0x80000000 will be marked
as a failure. Until we verify all userspace components are fixed,
revert this change.

Change-Id: I2eacbfb4f7b8fc9bf5704ca90d31c409819d7fbe
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>