um: Rework uaccess code

Rework UML's uaccess code to reuse as much as possible
from asm-generic/uaccess.c.

Signed-off-by: Richard Weinberger <richard@nod.at>

arch/x86/um/asm/segment.h

@@ -7,4 +7,12 @@ extern int host_gdt_entry_tls_min;
 #define GDT_ENTRY_TLS_MIN host_gdt_entry_tls_min
 #define GDT_ENTRY_TLS_MAX (GDT_ENTRY_TLS_MIN + GDT_ENTRY_TLS_ENTRIES - 1)
 
+typedef struct {
+	unsigned long seg;
+} mm_segment_t;
+
+#define MAKE_MM_SEG(s)	((mm_segment_t) { (s) })
+#define KERNEL_DS	MAKE_MM_SEG(~0UL)
+#define USER_DS		MAKE_MM_SEG(TASK_SIZE)
+
 #endif