build: skip driver symlinks without sub-directory

if user gives option -Ddrivers_install_subdir= or
-Ddrivers_install_subdir=. to install all the PMDs in
parent directory, The post installation script
"symlink-drivers-solibs.sh" can create invalid library file
named 'librte_*.so*' or meson installation errors:

ln: './librte_*' and './librte_*' are the same file
FAILED: install script '/bin/sh /home/nxa12342/upstream/dpdk/config/.
/buildtools/symlink-drivers-solibs.sh lib/x86_64-linux-gnu .' exit code 1,
stopped
FAILED: meson-install

This patch removes this post-install script execution to symlink
the PMDs libraries when no sub directory is given.

Signed-off-by: Gagandeep Singh <g.singh@nxp.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>

config/meson.build

@@ -95,8 +95,11 @@ eal_pmd_path = join_paths(get_option('prefix'), driver_install_path)
 # e.g. ixgbe depends on librte_bus_pci. This means that the bus drivers need
 # to be in the library path, so symlink the drivers from the main lib directory.
 if not is_windows
-    meson.add_install_script('../buildtools/symlink-drivers-solibs.sh',
-            get_option('libdir'), pmd_subdir_opt)
+    # skip symlink-drivers-solibs.sh execution on no sub directory
+    if pmd_subdir_opt != '' and pmd_subdir_opt != '.'
+        meson.add_install_script('../buildtools/symlink-drivers-solibs.sh',
+                get_option('libdir'), pmd_subdir_opt)
+    endif
 else
     meson.add_install_script(py3,
             files('../buildtools/symlink-drivers-solibs.py'),