ARM: 8543/1: decompressor: rename suffix_y to compress-y

The "$(suffix_y)" no longer appears in the file names, but it just
specifies the method of the file compression.  The "compress-y" sounds
more suitable.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>