library: move to platform

Library folder is just set of some mock platform definitions, so it
should be handled as another (abstract) platform.
It's better to have all platform definitions in platform folder
instead of adding some artifical platform to the src root.

Signed-off-by: Janusz Jankowski <janusz.jankowski@linux.intel.com>

src/arch/host/CMakeLists.txt

@@ -3,7 +3,7 @@ set(GENERATED_DIRECTORY ${PROJECT_BINARY_DIR}/generated)
 file(MAKE_DIRECTORY ${GENERATED_DIRECTORY}/include)
 
 target_include_directories(sof_options INTERFACE ${PROJECT_SOURCE_DIR}/src/arch/host/include)
-target_include_directories(sof_options INTERFACE ${PROJECT_SOURCE_DIR}/src/library/include)
+target_include_directories(sof_options INTERFACE ${PROJECT_SOURCE_DIR}/src/platform/library/include)
 target_include_directories(sof_options INTERFACE ${GENERATED_DIRECTORY}/include)
 
 # TODO: add Kconfig support also for testbench when it'll be decoupled from fw