base: introduce caching attributes (fix #1184)

On ARM it's relevant to not only distinguish between ordinary cached memory
and write-combined one, but also having non-cached memory too. To insert the
appropriated page table entries e.g.: in the base-hw kernel, we need to preserve
the information about the kind of memory from allocation until the pager
resolves a page fault. Therefore, this commit introduces a new Cache_attribute
type, and replaces the write_combined boolean with the new type where necessary.

repos/base-codezero/include/base/ipc_pager.h

@@ -14,6 +14,7 @@
 #ifndef _INCLUDE__BASE__IPC_PAGER_H_
 #define _INCLUDE__BASE__IPC_PAGER_H_
 
+#include <base/cache.h>
 #include <base/ipc.h>
 #include <base/stdint.h>
 #include <base/native_types.h>
@@ -37,7 +38,7 @@ namespace Genode {
 			 * Constructor
 			 */
 			Mapping(addr_t dst_addr, addr_t src_addr,
-			        bool write_combined, bool io_mem,
+			        Cache_attribute const cacheability, bool io_mem,
 			        unsigned l2size = PAGE_SIZE_LOG2,
 			        bool rw = true)
 			: