lib: Sparc's strncpy_from_user is generic enough, move under lib/

To use this, an architecture simply needs to:

1) Provide a user_addr_max() implementation via asm/uaccess.h

2) Add "select GENERIC_STRNCPY_FROM_USER" to their arch Kcnfig

3) Remove the existing strncpy_from_user() implementation and symbol
   exports their architecture had.

Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: David Howells <dhowells@redhat.com>

lib/Kconfig

@@ -16,6 +16,9 @@ config BITREVERSE
 config RATIONAL
 	boolean
 
+config GENERIC_STRNCPY_FROM_USER
+	bool
+
 config GENERIC_FIND_FIRST_BIT
 	bool