cmake: move find-modules to root cmake dir

CMakeModules/Findzstd.cmake

@@ -0,0 +1,26 @@
+# SPDX-FileCopyrightText: 2022 yuzu Emulator Project
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+include(FindPackageHandleStandardArgs)
+
+find_package(zstd QUIET CONFIG)
+if (zstd_CONSIDERED_CONFIGS)
+    find_package_handle_standard_args(zstd CONFIG_MODE)
+else()
+    find_package(PkgConfig QUIET)
+    pkg_search_module(ZSTD QUIET IMPORTED_TARGET libzstd)
+    find_package_handle_standard_args(zstd
+        REQUIRED_VARS ZSTD_LINK_LIBRARIES
+        VERSION_VAR ZSTD_VERSION
+    )
+endif()
+
+if (zstd_FOUND AND NOT TARGET zstd::zstd)
+    if (TARGET zstd::libzstd_shared)
+        add_library(zstd::zstd ALIAS zstd::libzstd_shared)
+    elseif (TARGET zstd::libzstd_static)
+        add_library(zstd::zstd ALIAS zstd::libzstd_static)
+    else()
+        add_library(zstd::zstd ALIAS PkgConfig::ZSTD)
+    endif()
+endif()