ARM: 6750/1: improvements to compressed/head.S

In the case of a conflict between the memory used by the compressed
kernel with its decompressor code and the memory used for the
decompressed kernel, we currently store the later after the former and
relocate it afterwards.

This would be more efficient to do this the other way around i.e.
relocate the compressed data up front instead, resulting in a smaller
copy.  That also has the advantage of making the code smaller and more
straight forward.

Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>