Additional Makefile fixes for Solaris 2.8

On Solaris, 'head' doesn't take a -q argument.  But we can use 'grep -h'
instead, so do that in Makefile.mod{inst,post}.  The built-in test to
/bin/sh doesn't like 'if ! cmd' syntax, so when determining if we need
to do modversion stuff, invert the if/else cases.  The built-in test
also doesn't understand -ef, so invoke a real version of test which does.
Signed-off-by: Tom Rini <trini@kernel.crashing.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>