modprobe: add --show-exports

modprobe: add --show-exports

modprobe has --show-modversions switch, which dumps symbols with
their modversion crcs from the __versions sections.

At the moment the section contains information for the dependency
symbols only, while exported symbols add to symtab entries with
__crc_ prefix (the format may differ, see 1e48901166ef libkmod-elf:
resolve CRC if module is built with MODULE_REL_CRCS).

The patch makes it to show exported symbols as well.

The function is basically cut'n'paste of show_modversions(),
but 'version' family replaced with 'symbol' one.

Signed-off-by: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>