Add 32 bit version of plat_get_syscnt_freq

Added plat_get_syscnt_freq2, which is a 32 bit variant of the 64 bit
plat_get_syscnt_freq. The old one has been flagged as deprecated.
Common code has been updated to use this new version. Porting guide
has been updated.

Change-Id: I9e913544926c418970972bfe7d81ee88b4da837e
diff --git a/plat/common/aarch64/plat_common.c b/plat/common/aarch64/plat_common.c
index 9070c61..4322341 100644
--- a/plat/common/aarch64/plat_common.c
+++ b/plat/common/aarch64/plat_common.c
@@ -40,6 +40,9 @@
 #pragma weak bl31_plat_enable_mmu
 #pragma weak bl32_plat_enable_mmu
 #pragma weak bl31_plat_runtime_setup
+#if !ERROR_DEPRECATED
+#pragma weak plat_get_syscnt_freq2
+#endif /* ERROR_DEPRECATED */
 
 void bl31_plat_enable_mmu(uint32_t flags)
 {
@@ -74,3 +77,14 @@
 }
 #endif
 
+
+#if !ERROR_DEPRECATED
+unsigned int plat_get_syscnt_freq2(void)
+{
+	unsigned long long freq = plat_get_syscnt_freq();
+
+	assert(freq >> 32 == 0);
+
+	return (unsigned int)freq;
+}
+#endif /* ERROR_DEPRECATED */