FROMLIST: arm64: mm: update max_pfn after memory hotplug

After new memory blocks have been hotplugged, max_pfn and max_low_pfn
needs updating to reflect on new PFNs being hot added to system.
Without this patch, debug-related functions that use max_pfn such as
get_max_dump_pfn() or read_page_owner() will not work with any page in
memory that is hot-added after boot.

Link: https://lore.kernel.org/lkml/cover.1632853776.git.quic_cgoldswo@quicinc.com/T/#md084740c6377eb12369bfe6eb8786f4689dc8498


Bug: 200171991
Fixes: 4ab21506 ("arm64: Add memory hotplug support")
Signed-off-by: Sudarshan Rajagopalan <quic_sudaraja@quicinc.com>
Signed-off-by: Chris Goldsworthy <quic_cgoldswo@quicinc.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Georgi Djakov <quic_c_gdjako@quicinc.com>
Change-Id: I1cb50889299957c871c498e19aa05778c7583c9d