Move PMU functions from pmu_ethosu.h to ethosu_pmu.c

This change is done as a prerequisite to be able to set
base address for NPU through ethosu_init(). So instead of using
a mamory mapped struct we use the same functions to read/write
PMU registers as the rest of the ethos-u driver.

Change-Id: Ie1f6e6af4627cbe9375e2b2d079ba8017b6294d3
diff --git a/src/ethosu_common.h b/src/ethosu_common.h
index 58fa1c6..7c33470 100644
--- a/src/ethosu_common.h
+++ b/src/ethosu_common.h
@@ -48,6 +48,9 @@
 #define VER_STR(X) VNUM_STR(X)
 #define VNUM_STR(X) #X
 
+#define MASK_0_31_BITS (0xFFFFFFFF)
+#define MASK_32_47_BITS (0xFFFF00000000)
+
 static const __attribute__((section("npu_driver_version"))) char driver_version_str[] = VER_STR(
     ETHOSU_DRIVER_VERSION_MAJOR) "." VER_STR(ETHOSU_DRIVER_VERSION_MINOR) "." VER_STR(ETHOSU_DRIVER_VERSION_PATCH);