qlnxr: cleanup secondary effects from EOL purge

DEFINE_ALLOC_MR became unconditionally true, but it isn't used anywhere
now. Several places depended upon DEFINE_IB_FAST_REG, but that is now
always false.
Similarly DEFINE_IB_UMEM_WITH_CHUNK became always false/undefined.
DEFINE_IB_AH_ATTR_WITH_DMAC is now unconditionally true.

Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/603
Differential Revision: https://reviews.freebsd.org/D35560