powerpc: module: handle MODVERSION for .TOC.

For the ELFv2 ABI, powerpc introduces a magic symbol ".TOC.".  If we
don't create a CRC for it (minus the leading ".", since we strip that)
we get a modpost warning about missing CRC and the CRC array seems to
be displaced by 1 so other CRCs mismatch too.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>