ARCv2: entry: rewrite to enable use of double load/stores LDD/STD

- the motivation was to be remove blatent copy-paste due to hasty support
   of CONFIG_ARC_IRQ_NO_AUTOSAVE support

 - but with refactoring we could use LDD/STD to greatly optimize the code

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/include/asm/linkage.h

@@ -10,6 +10,24 @@
 
 #ifdef __ASSEMBLY__
 
+.macro ST2 e, o, off
+#ifdef CONFIG_ARC_HAS_LL64
+	std	\e, [sp, \off]
+#else
+	st	\e, [sp, \off]
+	st	\o, [sp, \off+4]
+#endif
+.endm
+
+.macro LD2 e, o, off
+#ifdef CONFIG_ARC_HAS_LL64
+	ldd	\e, [sp, \off]
+#else
+	ld	\e, [sp, \off]
+	ld	\o, [sp, \off+4]
+#endif
+.endm
+
 #define ASM_NL		 `	/* use '`' to mark new line in macro */
 
 /* annotation for data we want in DCCM - if enabled in .config */