xtensa: reorganize SR referencing

- reference SRs by names where possible, not by numbers;
- get rid of __stringify around SR names where possible;
- remove unneeded SR names from asm/regs.h;
- add SREG_ prefix to remaining SR names;

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>

arch/xtensa/platforms/iss/setup.c

@@ -61,13 +61,13 @@ void platform_restart(void)
 	 * jump to the reset vector. */
 
 	__asm__ __volatile__("movi	a2, 15\n\t"
-			     "wsr	a2, " __stringify(ICOUNTLEVEL) "\n\t"
+			     "wsr	a2, icountlevel\n\t"
 			     "movi	a2, 0\n\t"
-			     "wsr	a2, " __stringify(ICOUNT) "\n\t"
-			     "wsr	a2, " __stringify(IBREAKENABLE) "\n\t"
-			     "wsr	a2, " __stringify(LCOUNT) "\n\t"
+			     "wsr	a2, icount\n\t"
+			     "wsr	a2, ibreakenable\n\t"
+			     "wsr	a2, lcount\n\t"
 			     "movi	a2, 0x1f\n\t"
-			     "wsr	a2, " __stringify(PS) "\n\t"
+			     "wsr	a2, ps\n\t"
 			     "isync\n\t"
 			     "jx	%0\n\t"
 			     :