kernel: mmu: exclude some funcs from coverage

page_frame_dump() and z_page_frames_dump() are used for
debug print, so there is no need to cover those funcs.
__weak function is also excluded, every test overrides it.

Signed-off-by: Lixin Guo <lixinx.guo@intel.com>
diff --git a/kernel/mmu.c b/kernel/mmu.c
index e7c090f..558bff9 100644
--- a/kernel/mmu.c
+++ b/kernel/mmu.c
@@ -72,6 +72,7 @@
 #define COLOR(x)	do { } while (0)
 #endif
 
+/* LCOV_EXCL_START */
 static void page_frame_dump(struct z_page_frame *pf)
 {
 	if (z_page_frame_is_reserved(pf)) {
@@ -120,6 +121,7 @@
 		printk("\n");
 	}
 }
+/* LCOV_EXCL_STOP */
 
 #define VIRT_FOREACH(_base, _size, _pos) \
 	for (_pos = _base; \
@@ -417,6 +419,7 @@
 	pf->addr = addr;
 }
 
+/* LCOV_EXCL_START */
 /* Go through page frames to find the physical address mapped
  * by a virtual address.
  *
@@ -445,6 +448,8 @@
 
 	return ret;
 }
+/* LCOV_EXCL_STOP */
+
 __weak FUNC_ALIAS(virt_to_page_frame, arch_page_phys_get, int);
 
 #ifdef CONFIG_DEMAND_PAGING