csky: uaccess.h: Coding convention with asm generic

Using asm-generic/uaccess.h to prevent duplicated code:
 - Add user_addr_max which mentioned in generic uaccess.h
 - Remove custom definitions of KERNEL/USER_DS, get/set_fs,
   uaccess_kerenl
 - Using generic extable.h instead of custom definitions in
   uaccess.h

Change v2:
 - Fixup tinyconfig compile error, "__put_user_bad"
 - Add __get_user_asm_64
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Link: https://lore.kernel.org/linux-csky/CAK8P3a1DvsXSEDoovLk11hzNHyJi7vqNoToU+n5aFi2viZO_Uw@mail.gmail.com/T/#mbcd58a0e3450e5598974116b607589afa16a3ab7
Cc: Arnd Bergmann <arnd@arndb.de>

arch/csky/include/asm/Kbuild

 # SPDX-License-Identifier: GPL-2.0
 generic-y += asm-offsets.h
+generic-y += extable.h
 generic-y += gpio.h
 generic-y += kvm_para.h
 generic-y += qrwlock.h

arch/csky/include/asm/segment.h

@@ -7,11 +7,4 @@ typedef struct {
 	unsigned long seg;
 } mm_segment_t;
 
-#define KERNEL_DS		((mm_segment_t) { 0xFFFFFFFF })
-
-#define USER_DS			((mm_segment_t) { PAGE_OFFSET })
-#define get_fs()		(current_thread_info()->addr_limit)
-#define set_fs(x)		(current_thread_info()->addr_limit = (x))
-#define uaccess_kernel()	(get_fs().seg == KERNEL_DS.seg)
-
 #endif /* __ASM_CSKY_SEGMENT_H */

arch/csky/mm/fault.c

@@ -12,7 +12,7 @@ int fixup_exception(struct pt_regs *regs)
 
 	fixup = search_exception_tables(instruction_pointer(regs));
 	if (fixup) {
-		regs->pc = fixup->nextinsn;
+		regs->pc = fixup->fixup;
 
 		return 1;
 	}