CONFIG: Move libibverbs detection into UCX_CHECK_VERBS macro (#11736)

Extract the --with-verbs option processing and basic libibverbs detection
from src/uct/ib/configure.m4 into a standalone UCX_CHECK_VERBS macro in
config/m4/verbs.m4, following the UCX_CHECK_CUDA pattern.

Co-authored-by: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>