Fix MISRA Rule 5.7 Part 1

Rule 5.7: A tag name shall be a unique identifier

There were 2 amu_ctx struct type definitions:
    - In lib/extensions/amu/aarch64/amu.c
    - In lib/cpus/aarch64/cpuamu.c

Renamed the latter to cpuamu_ctx to avoid this name clash

To avoid violation of Rule 8.3 also change name of function
amu_ctxs to unique name (cpuamu_ctxs) since it now returns a
different type (cpuamu_ctx) than the other amu_ctxs function

Fixed for:
    make LOG_LEVEL=50 PLAT=fvp

Change-Id: Ieeb7e390ec2900fd8b775bef312eda93804a43ed
Signed-off-by: Daniel Boulby <daniel.boulby@arm.com>

lib/cpus/aarch64/cpuamu.c

@@ -10,12 +10,12 @@
 
 #define CPUAMU_NR_COUNTERS	5U
 
-struct amu_ctx {
+struct cpuamu_ctx {
 	uint64_t cnts[CPUAMU_NR_COUNTERS];
 	unsigned int mask;
 };
 
-static struct amu_ctx amu_ctxs[PLATFORM_CORE_COUNT];
+static struct cpuamu_ctx cpuamu_ctxs[PLATFORM_CORE_COUNT];
 
 int midr_match(unsigned int cpu_midr)
 {
@@ -29,7 +29,7 @@ int midr_match(unsigned int cpu_midr)
 
 void cpuamu_context_save(unsigned int nr_counters)
 {
-	struct amu_ctx *ctx = &amu_ctxs[plat_my_core_pos()];
+	struct cpuamu_ctx *ctx = &cpuamu_ctxs[plat_my_core_pos()];
 	unsigned int i;
 
 	assert(nr_counters <= CPUAMU_NR_COUNTERS);
@@ -48,7 +48,7 @@ void cpuamu_context_save(unsigned int nr_counters)
 
 void cpuamu_context_restore(unsigned int nr_counters)
 {
-	struct amu_ctx *ctx = &amu_ctxs[plat_my_core_pos()];
+	struct cpuamu_ctx *ctx = &cpuamu_ctxs[plat_my_core_pos()];
 	unsigned int i;
 
 	assert(nr_counters <= CPUAMU_NR_COUNTERS);