package/irqbalance: use pkg-config to find numa

Use pkg-config to find numa to avoid the following build failure when
checking for numa_available:

configure:9667: checking for numa_available in -lnuma
configure:9692: /tmp/instance-7/output-1/host/bin/microblazeel-linux-gcc -o conftest -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -Os   -static -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -static conftest.c -lnuma   >&5
/tmp/instance-7/output-1/host/opt/ext-toolchain/bin/../lib/gcc/microblazeel-buildroot-linux-uclibc/9.3.0/../../../../microblazeel-buildroot-linux-uclibc/bin/ld: /tmp/instance-7/output-1/host/microblazeel-buildroot-linux-uclibc/sysroot/usr/lib/libnuma.a(libnuma.o): in function `numa_node_to_cpus_v1':
(.text+0x2a80): undefined reference to `__atomic_fetch_and_1'
/tmp/instance-7/output-1/host/opt/ext-toolchain/bin/../lib/gcc/microblazeel-buildroot-linux-uclibc/9.3.0/../../../../microblazeel-buildroot-linux-uclibc/bin/ld: /tmp/instance-7/output-1/host/microblazeel-buildroot-linux-uclibc/sysroot/usr/lib/libnuma.a(libnuma.o): in function `numa_node_to_cpus_v2':
(.text+0x2ddc): undefined reference to `__atomic_fetch_and_1'
collect2: error: ld returned 1 exit status

Fixes:
 - http://autobuild.buildroot.org/results/577a63432fba2f9ae1ed2c6c2a77c5ce54ac5521



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>