drm_hwcomposer: clang-tidy: enable cppcoreguidelines-* checks

Our code isn't ready for the following checks therefore keep disabled
-cppcoreguidelines-pro-bounds-array-to-pointer-decay
-cppcoreguidelines-pro-bounds-constant-array-index
-cppcoreguidelines-pro-bounds-pointer-arithmetic
-cppcoreguidelines-pro-type-cstyle-cast
-cppcoreguidelines-pro-type-vararg
-cppcoreguidelines-avoid-magic-numbers
-cppcoreguidelines-macro-usage
-cppcoreguidelines-avoid-c-arrays

+ fixed existing tidy warnings for these checks.

Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
diff --git a/backend/Backend.cpp b/backend/Backend.cpp
index 15a9ff1..16e2859 100644
--- a/backend/Backend.cpp
+++ b/backend/Backend.cpp
@@ -63,7 +63,7 @@
     size_t extra_client = (z_map.size() - client_size) - avail_planes;
     if (extra_client > 0) {
       int start = 0;
-      size_t steps;
+      size_t steps = 0;
       if (client_size != 0) {
         size_t prepend = std::min((size_t)client_start, extra_client);
         size_t append = std::min(z_map.size() - (client_start + client_size),
@@ -136,6 +136,7 @@
           display->resource_manager()->ForcedScalingWithGpu());
 }
 
+// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
 REGISTER_BACKEND("generic", Backend);
 
 }  // namespace android