armvirt: 32: enable CONFIG_ARM_LPAE

armvirt: 32: enable CONFIG_ARM_LPAE

This is required for running armvirt_32 on QEMU 3.0 [1], otherwise the
kernel will emit the following complaint and virtio-net-pci devices will
fail to be initialized

        [    1.124214] OF: PCI: host bridge /pcie@10000000 ranges:
        [    1.125093] OF: PCI:    IO 0x3eff0000..0x3effffff -> 0x00000000
        [    1.125942] OF: PCI:   MEM 0x10000000..0x3efeffff -> 0x10000000
        [    1.126403] OF: PCI:   MEM 0x8000000000..0xffffffffff -> 0x8000000000
        [    1.127748] pci-host-generic 4010000000.pcie: can't claim ECAM area [mem 0x10000000-0x1fffffff]: address conflict with /pcie@10000000 [mem 0x10000000-0x3efeffff]
        [    1.129752] pci-host-generic: probe of 4010000000.pcie failed with error -16

Running QEMU with "-M virt,highmem=off" is an option, but "highmem" was only
introduced as a default on flag since QEMU 2.5.0 and QEMU will fail and quit on
encounter of unknown flags

 [1] Armv7 guest fails to boot with qemu-3.0.0-1,
     https://bugzilla.redhat.com/show_bug.cgi?id=1633328#c5

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>