Install CMake files in MbedTLS dir

Right now, CMake files are installed in <prefix>/cmake. That being said,
it gets easily bloated, and the standard is to use a directory with the
same name as the project.

I discovered this issue with this "bug":
https://github.com/termux/termux-packages/issues/12416
The issue's author claimed that MbedTLS's files were not installed in
the lib directory. But the patch applied by termux team broke CMake's
search of MbedTLS config files. So I wanted to upstream the real fix
here instead.

Here are some examples of projects using directories:
 - https://github.com/xiph/flac/blob/1.4.2/CMakeLists.txt#L239
 - https://gitlab.freedesktop.org/dbus/dbus/-/blob/dbus-1.15.2/CMakeLists.txt#L675
 - https://github.com/catchorg/Catch2/blob/v3.2.0/CMakeLists.txt#L62
 - https://github.com/capnproto/capnproto/blob/v0.10.2/c++/CMakeLists.txt#L162

Signed-off-by: Issam E. Maghni <issam.e.maghni@mailbox.org>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 59a960a..f72de64 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -355,7 +355,7 @@
     install(
         FILES "${CMAKE_CURRENT_BINARY_DIR}/cmake/MbedTLSConfig.cmake"
               "${CMAKE_CURRENT_BINARY_DIR}/cmake/MbedTLSConfigVersion.cmake"
-        DESTINATION "cmake")
+        DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/MbedTLS")
 
     export(
         EXPORT MbedTLSTargets
@@ -365,7 +365,7 @@
     install(
         EXPORT MbedTLSTargets
         NAMESPACE MbedTLS::
-        DESTINATION "cmake"
+        DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/MbedTLS"
         FILE "MbedTLSTargets.cmake")
 
     if(CMAKE_VERSION VERSION_GREATER 3.15 OR CMAKE_VERSION VERSION_EQUAL 3.15)