ARM: 9154/1: decompressor: do not copy source files while building

As commit 7ae4a78d

 ("ARM: 8969/1: decompressor: simplify libfdt
builds") stated, copying source files during the build time may not
end up with as clean code as expected.

Do similar for the other library files for further cleanups of the
Makefile and .gitignore.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>