tests: fix some issues when enabling coverage for qemu_x86_64

Fix some issues in linker.ld when enabling coverage report feature
for qemu_x86_64 platform:
1. Fix the gcov record data should not be in BSS section.
2. Fix some test case crash due to lack of memory page align before
gcov rodata.

Signed-off-by: Enjia Mai <enjiax.mai@intel.com>