m68k: uapi: Add ucontext.h

ucontext.h should be an UAPI header as it is used for the kernel's
signal handling interface.

Move the header to the uapi/ directory.

While at it, also add some necessary includes to the new header.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://patch.msgid.link/20260314-uapi-ucontext-m68k-v1-1-1b8b0e082b79@weissschuh.net
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

Author: t-8ch

arch/m68k/include/asm/ucontext.h arch/m68k/include/uapi/asm/ucontext.harch/m68k/include/asm/ucontext.h renamed to arch/m68k/include/uapi/asm/ucontext.h

@@ -1,7 +1,10 @@
-/* SPDX-License-Identifier: GPL-2.0 */
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
 #ifndef _M68K_UCONTEXT_H
 #define _M68K_UCONTEXT_H
 
+#include <asm/sigcontext.h>
+#include <asm/signal.h>
+
 typedef int greg_t;
 #define NGREG 18
 typedef greg_t gregset_t[NGREG];