meson: adjust nlohmann-json dependency

Simplify the meson directive for nlohmann-json dependency and rename the
wrap file to align with other repositories.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I6ad9d4fe3e8fa24673b736bab81e2fcabc51f1a0
diff --git a/extensions/openpower-pels/meson.build b/extensions/openpower-pels/meson.build
index 1cf9839..f1c10f1 100644
--- a/extensions/openpower-pels/meson.build
+++ b/extensions/openpower-pels/meson.build
@@ -3,11 +3,7 @@
     default_options: ['oem-ibm=enabled'],
 )
 
-if cpp.has_header('nlohmann/json.hpp')
-    nlohmann_json_dep = declare_dependency()
-else
-    nlohmann_json_dep = dependency('nlohmann-json')
-endif
+nlohmann_json_dep = dependency('nlohmann_json', include_type: 'system')
 
 python_inst = import('python').find_installation('python3')
 python_ver = python_inst.language_version()