arm64: defconfig: Enable CONFIG_SPARSEMEM_VMEMMAP on Lahaina

Enable CONFIG_SPARSEMEM_VMEMMAP for more performant
pfn_to_page() and page_to_pfn() operations.

Change-Id: If70aa5d2d9bc235fb4426c8648b740bb890c6e9a
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>