libkmod-elf: resolve CRC if module is built with MODULE_REL_CRCS

libkmod-elf: resolve CRC if module is built with MODULE_REL_CRCS

Normally exported symbol's crc is stored as absolute (SHN_ABS)
value of special named symbol __crc_<symbol name>.

When the kernel and modules are built with the config option
CONFIG_MODULE_REL_CRCS, all the CRCs are put in a special section
and the __crc_<symbol name> symbols values are offsets in the
section. See patch description of the commit:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=56067812d5b0e737ac2063e94a50f76b810d6ca3

Add kmod support of this configuration.

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