build: Make sure isa-l is built prior building dependent libs

In case SPDK is built with --with-dpdk[=*] rather than the submodule
it starts building libs and isa-l together leading to:

  SO libspdk_util.so.5.1
  /usr/bin/ld.bfd: cannot find -lisal
  collect2: error: ld returned 1 exit status
  make[2]: *** [/root/spdk/mk/spdk.lib.mk:86:
  /root/spdk/build/lib/libspdk_util.so.5.1] Error 1
  make[1]: *** [/root/spdk/mk/spdk.subdirs.mk:16: util] Error 2
  make: *** [/root/spdk/mk/spdk.subdirs.mk:16: lib] Error 2

To avoid this make sure that isa-l, being a hard dependency now, is
always build before anything else.

Signed-off-by: Michal Berger <michal.berger@intel.com>
Change-Id: I933900a756924458324062cd740d99e5ccb370f6
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/14621


Reviewed-by: Pawel Piatek <pawelx.piatek@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com>
Reviewed-by: Aleksey Marchuk <alexeymar@nvidia.com>
Community-CI: Mellanox Build Bot
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>