streamline_config.pl: handle also ${CONFIG_FOO}

streamline_config.pl currently searches for CONFIG options in Kconfig
files as $(CONFIG_FOO). But some Kconfigs (e.g. thunderbolt) use
${CONFIG_FOO}. So fix up the regex to accept both.

This fixes:
$ make LSMOD=`pwd/`/lsmod localmodconfig
using config: '.config'
thunderbolt config not found!!

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>