[uaccess] Reduce scope of included uaccess.h header

The uaccess.h header is no longer required for any code that touches
external ("user") memory, since such memory accesses are now performed
through pointer dereferences.  Reduce the number of files including
this header.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/x86/image/elfboot.c

@@ -30,6 +30,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #include <ipxe/elf.h>
 #include <ipxe/features.h>
 #include <ipxe/init.h>
+#include <ipxe/uaccess.h>
 
 /**
  * @file

src/arch/x86/image/pxe_image.c

@@ -34,7 +34,6 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #include <pxe.h>
 #include <pxe_call.h>
 #include <pic8259.h>
-#include <ipxe/uaccess.h>
 #include <ipxe/image.h>
 #include <ipxe/segment.h>
 #include <ipxe/netdevice.h>

src/arch/x86/interface/pxe/pxe_file.c

@@ -8,7 +8,6 @@
 #include <stdio.h>
 #include <errno.h>
 #include <byteswap.h>
-#include <ipxe/uaccess.h>
 #include <ipxe/posix_io.h>
 #include <ipxe/features.h>
 #include <pxe.h>