csky: Reconstruct signal processing

Linux kernel has provided some apis for arch signal's implementation.
For example:
	restore_saved_sigmask()
	set_current_blocked()
	restore_altstack()

But in last version of csky signal.c didn't use them and some codes are
confusing, so reconstruct signal.c with reference to riscv's code.

Now csky signal.c implementation are very close to riscv and we can
get the following benefits:
 - Clear code structure
 - The signal code of riscv and csky can be reviewed together
 - Promoting the unification of arch's signal implementation

Also modified the related code in entry.S

Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Cc: Arnd Bergmann <arnd@arndb.de>

arch/csky/abiv2/inc/abi/entry.h

@@ -14,18 +14,11 @@
 #define LSAVE_A2	32
 #define LSAVE_A3	36
 
-#define EPC_INCREASE	4
-#define EPC_KEEP	0
-
 #define KSPTOUSP
 #define USPTOKSP
 
 #define usp cr<14, 1>
 
-.macro INCTRAP	rx
-	addi	\rx, EPC_INCREASE
-.endm
-
 .macro SAVE_ALL epc_inc
 	subi    sp, 152
 	stw	tls, (sp, 0)

arch/csky/abiv2/inc/abi/regdef.h

@@ -21,4 +21,6 @@
 
 #define SYSTRACE_SAVENUM	5
 
+#define TRAP0_SIZE		4
+
 #endif /* __ASM_CSKY_REGDEF_H */