meson: Fix deprecated meson warnings

Fix the warnings related to deprecated meson functions:

WARNING: Project targeting '>= 0.57.0' but tried to use feature deprecated since '0.56.0': Dependency.get_pkgconfig_variable. use Dependency.get_variable(pkgconfig : ...) instead
WARNING: Project targeting '>= 0.57.0' but tried to use feature deprecated since '0.56.0': meson.source_root. use meson.project_source_root() or meson.global_source_root() instead.

Tested: Verify that there are no such warnings in local CI.

Signed-off-by: Lei YU <yulei.sh@bytedance.com>
Change-Id: I1388aaa12161d020d06657e507ddef78cb116ffe
diff --git a/meson.build b/meson.build
index 1367a72..f6f3f35 100644
--- a/meson.build
+++ b/meson.build
@@ -150,7 +150,7 @@
 ssl = dependency('openssl')
 
 systemd = dependency('systemd')
-systemd_system_unit_dir = systemd.get_pkgconfig_variable('systemdsystemunitdir')
+systemd_system_unit_dir = systemd.get_variable(pkgconfig : 'systemdsystemunitdir')
 
 unit_files = [
     'obmc-flash-bmc-setenv@.service.in',
diff --git a/usb/meson.build b/usb/meson.build
index b8a138a..bb1dc60 100644
--- a/usb/meson.build
+++ b/usb/meson.build
@@ -40,12 +40,12 @@
     install_dir: get_option('bindir')
 )
 
-systemd_system_unit_dir = dependency('systemd').get_pkgconfig_variable(
-    'systemdsystemunitdir',
-    define_variable: ['prefix', get_option('prefix')])
-udev_dir = dependency('udev').get_pkgconfig_variable(
-    'udev_dir',
-    define_variable: ['prefix', get_option('prefix')])
+systemd_system_unit_dir = dependency('systemd').get_variable(
+    pkgconfig: 'systemdsystemunitdir',
+    pkgconfig_define: ['prefix', get_option('prefix')])
+udev_dir = dependency('udev').get_variable(
+    pkgconfig: 'udev_dir',
+    pkgconfig_define: ['prefix', get_option('prefix')])
 
 install_data(
     'services/usb-code-update@.service',
diff --git a/xyz/openbmc_project/Software/Image/meson.build b/xyz/openbmc_project/Software/Image/meson.build
index 4ae382f..0783a60 100644
--- a/xyz/openbmc_project/Software/Image/meson.build
+++ b/xyz/openbmc_project/Software/Image/meson.build
@@ -3,7 +3,7 @@
     capture: true,
     command: [
         sdbusplusplus_prog,
-        '-r', meson.source_root(),
+        '-r', meson.project_source_root(),
         'error',
         'exception-header',
         'xyz.openbmc_project.Software.Image',
@@ -19,7 +19,7 @@
     capture: true,
     command: [
         sdbusplusplus_prog,
-        '-r', meson.source_root(),
+        '-r', meson.project_source_root(),
         'error',
         'exception-cpp',
         'xyz.openbmc_project.Software.Image',