arm64: To remove initrd reserved area entry from memblock

INITRD reserved area entry is not removed from memblock
even though initrd reserved area is freed. After freeing
the memory it is released from memblock. The same can be
checked from /sys/kernel/debug/memblock/reserved.

The patch makes sure that the initrd entry is removed from
memblock when keepinitrd is not enabled.

The patch only affects accounting and debugging. This does not
fix any memory leak.

Acked-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: CHANDAN VN <chandan.vn@samsung.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>