soc: qcom: mem-offline: online only valid memory blocks

mem-offline driver onlines blocks between memory_limit to end of DDR,
but for some cases when using large ram size, the range may not be
contiguous. We online un-existed memory blocks in this case. Example
-
RAM Entry 0 : Base 0x0080000000  Size 0x0033E00000
RAM Entry 1 : Base 0x0200000000  Size 0x0200000000
RAM Entry 2 : Base 0x0800000000  Size 0x0100000000
RAM Entry 3 : Base 0x00C0000000  Size 0x0140000000
if offline-size is 5GB and total memory size is 18GB, we onlined
also un-existed range [0x400000000,0x800000000] in
mem_online_remaining_blocks(). To fix this, Do parsing the DT tree
again and updated bitmap accordingly. Use this bitmap to online memory
blocks.

Change-Id: I5ea94a0ea9dca10e3a3311d6ea53a14302a41ae5
Signed-off-by: Zhenhua Huang <zhenhuah@codeaurora.org>