cnss: Fix reservation for CNSS memory hole

memblock-remove can only be safely used on 1MB alignments. To
avoid unpredictable behavior, use memreserve instead. Virtual
addresses will exist for the address range specified, but the
memory will not be otherwise used by the kernel.

CRs-Fixed: 689456
Change-Id: I6cc57f441bd6a13c473616f2a861a1484ac1ec47
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>