IA64: Use early_parm to handle mvec_name and nomca

I'm not sure of the worthiness of this idea, so please consider it an RFC.
Its key merits are:

* Reuse existing infrastructure
* Greatly tightens up the parsing of nomca
* Greatly simplifies the parsing of machvec

Addition cleanup (moving setup_mvec() to machvec.c) by Ken Chen.

Signed-Off-By: Horms <horms@verge.net.au>
Signed-Off-By: Tony Luck <tony.luck@intel.com>