migrate from req_ctx to msgb

We now generalize the USB communiction and abandon the 'req_ctx'
structure inherited from openpcd.  Instead we use the libosmocore 'msgb'
structure to handle incoming and outgoing USB tranfers.  We also use
linuxlist-based msgb-queues for each endpoint.

firmware/libcommon/include/talloc.h

@@ -0,0 +1,25 @@
+#pragma once
+
+#include <stdlib.h>
+#include <stdarg.h>
+
+/* minimalistic emulation of core talloc API functions used by msgb.c */
+
+#define __TALLOC_STRING_LINE1__(s)    #s
+#define __TALLOC_STRING_LINE2__(s)   __TALLOC_STRING_LINE1__(s)
+#define __TALLOC_STRING_LINE3__  __TALLOC_STRING_LINE2__(__LINE__)
+#define __location__ __FILE__ ":" __TALLOC_STRING_LINE3__
+
+#define talloc_zero(ctx, type) (type *)_talloc_zero(ctx, sizeof(type), #type)
+#define talloc_zero_size(ctx, size) _talloc_zero(ctx, size, __location__)
+void *_talloc_zero(const void *ctx, size_t size, const char *name);
+
+#define talloc_free(ctx) _talloc_free(ctx, __location__)
+int _talloc_free(void *ptr, const char *location);
+
+/* Unsupported! */
+#define talloc_size(ctx, size) talloc_named_const(ctx, size, __location__)
+void *talloc_named_const(const void *context, size_t size, const char *name);
+void talloc_set_name_const(const void *ptr, const char *name);
+char *talloc_strdup(const void *t, const char *p);
+void *talloc_pool(const void *context, size_t size);