ARM: 6093/1: Fix kernel memory printing for sparsemem

The show_mem() and mem_init() function are assuming that the page map is
contiguous and calculates the start and end page of a bank using (map +
pfn). This fails with SPARSEMEM where pfn_to_page() must be used.

Tested-by: Will Deacon <Will.Deacon@arm.com>
Tested-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>