MIPS: Optimize current_cpu_type() for better code.

 o Move current_cpu_type() to a separate header file
 o #ifdefing on supported CPU types lets modern GCC know that certain
   code in callers may be discarded ideally turning current_cpu_type() into
   a function returning a constant.
 o Use current_cpu_type() rather than direct access to struct cpuinfo_mips.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5833/
diff --git a/arch/mips/kernel/idle.c b/arch/mips/kernel/idle.c
index 42f8875..f7991d9 100644
--- a/arch/mips/kernel/idle.c
+++ b/arch/mips/kernel/idle.c
@@ -18,6 +18,7 @@
 #include <linux/sched.h>
 #include <asm/cpu.h>
 #include <asm/cpu-info.h>
+#include <asm/cpu-type.h>
 #include <asm/idle.h>
 #include <asm/mipsregs.h>
 
@@ -136,7 +137,7 @@
 		return;
 	}
 
-	switch (c->cputype) {
+	switch (current_cpu_type()) {
 	case CPU_R3081:
 	case CPU_R3081E:
 		cpu_wait = r3081_wait;