fix(lib/mbedtls): cmake rules and mbedtls targets

- Include targets from mbedtls/library instead of including top level
  CMakeLists.txt
- Move mbedtls configs to mbedtls_config.h
- Remove stale build option MbedTLS_BUILD_TYPE from documentation

Signed-off-by: Arunachalam Ganapathy <arunachalam.ganapathy@arm.com>
Change-Id: I7096ef6df9339c2c490450f72ec91b681b32543e
diff --git a/cmake/CommonConfigs.cmake b/cmake/CommonConfigs.cmake
index ea517a3..d8c3e68 100644
--- a/cmake/CommonConfigs.cmake
+++ b/cmake/CommonConfigs.cmake
@@ -93,7 +93,7 @@
 target_compile_definitions(rmm-common
     INTERFACE "RMM_NUM_PAGES_PER_STACK=UL(${RMM_NUM_PAGES_PER_STACK})")
 
-if(RMM_FPU_USE_AT_REL2)
+if(RMM_FPU_USE_AT_REL2 AND RMM_ARCH STREQUAL aarch64)
     target_compile_definitions(rmm-common
         INTERFACE "RMM_FPU_USE_AT_REL2=1")
 endif()