kbuild: add -fverbose-asm to i386 Makefile

Add -fverbose-asm to i386 Makefile rule for building .s files.  This makes
the assembler output much more readable for humans.

Suggested by Der Herr Hofrat <der.herr@hofr.at>

Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>