ARM: OMAP2+: Fix oops with LPAE and more than 2GB of memory

On boards with more than 2GB of RAM booting goes wrong with things not
working and we're getting lots of l3 warnings:

WARNING: CPU: 0 PID: 1 at drivers/bus/omap_l3_noc.c:147
l3_interrupt_handler+0x260/0x384()
44000000.ocp:L3 Custom Error: MASTER MMC6 TARGET DMM1 (Idle):
Data Access in User mode during Functional access
...
[<c044e158>] (scsi_add_host_with_dma) from [<c04705c8>]
(ata_scsi_add_hosts+0x5c/0x18c)
[<c04705c8>] (ata_scsi_add_hosts) from [<c046b13c>]
(ata_host_register+0x150/0x2cc)
[<c046b13c>] (ata_host_register) from [<c046b38c>]
(ata_host_activate+0xd4/0x124)
[<c046b38c>] (ata_host_activate) from [<c047f42c>]
(ahci_host_activate+0x5c/0x194)
[<c047f42c>] (ahci_host_activate) from [<c0480854>]
(ahci_platform_init_host+0x1f0/0x3f0)
[<c0480854>] (ahci_platform_init_host) from [<c047c9dc>]
(ahci_probe+0x70/0x98)
[<c047c9dc>] (ahci_probe) from [<c04220cc>]
(platform_drv_probe+0x54/0xb4)

Let's fix the issue by enabling ZONE_DMA for LPAE. Note that we need to
limit dma_zone_size to 2GB as the rest of the RAM is beyond the 4GB limit.

Let's also fix things for dra7 as done in similar patches in the TI tree
by Lokesh Vutla <lokeshvutla@ti.com>.

Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>