build: fix essential drivers in disable list

The PCI and vdev bus drivers cannot be disabled for DPDK builds and
special logic is put in place to not skip them when they are specified
in the disable list. This logic is broken though, as the inclusion of
the driver-specific meson.build file is only included in the "else" leg
of the condition check. This means that when they are specified as
disabled the PCI and vdev buses are not disabled, but neither are their
source files compiled.

Fix this by moving the "subdir()" call into the next "if build" block,
ensuring that if not disabled the sources are always included. To take
account of the fact that the subdir call could itself disable the
driver, we add a break call into the following loop to ensure we quickly
fall through to the following block which stops processing appropriately
if the driver is disabled.

Fixes: 2e33309ebe03 ("config: enable/disable drivers in Arm builds")
Cc: stable@dpdk.org

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Tested-by: Radu Nicolau <radu.nicolau@intel.com>
Acked-by: Radu Nicolau <radu.nicolau@intel.com>

drivers/meson.build

@@ -109,16 +109,19 @@ foreach subpath:subdirs
                 build = false
                 reason = 'explicitly disabled via build config'
             endif
-        else
-            # pull in driver directory which should update all the local variables
-            subdir(drv_path)
         endif
 
         if build
+            # pull in driver directory which should update all the local variables
+            subdir(drv_path)
+
             # get dependency objs from strings
             shared_deps = ext_deps
             static_deps = ext_deps
             foreach d:deps
+                if not build
+                    break
+                endif
                 if not is_variable('shared_rte_' + d)
                     build = false
                     reason = 'missing internal dependency, "@0@"'.format(d)