ARM: bL_switcher: Add synchronous enable/disable interface

Some subsystems will need to know for sure whether the switcher is
enabled or disabled during certain critical regions.

This patch provides a simple mutex-based mechanism to discover
whether the switcher is enabled and temporarily lock out further
enable/disable:

  * bL_switcher_get_enabled() returns true iff the switcher is
    enabled and temporarily inhibits enable/disable.

  * bL_switcher_put_enabled() permits enable/disable of the switcher
    again after a previous call to bL_switcher_get_enabled().

Signed-off-by: Dave Martin <dave.martin@linaro.org>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
diff --git a/arch/arm/include/asm/bL_switcher.h b/arch/arm/include/asm/bL_switcher.h
index 19757c0..bc23d1c 100644
--- a/arch/arm/include/asm/bL_switcher.h
+++ b/arch/arm/include/asm/bL_switcher.h
@@ -14,4 +14,7 @@
 
 int bL_switch_request(unsigned int cpu, unsigned int new_cluster_id);
 
+bool bL_switcher_get_enabled(void);
+void bL_switcher_put_enabled(void);
+
 #endif