[ARM] pxa: add basic support for Voipac PXA270 SBC

This patch adds basic support for the Voipac PXA270 SBC.
The device consists of the following hardware:
- PXA270 @ 520 MHz
- 256MB RAM (sparsemem, 2*128MB regions)
- 64MB NOR flash
- 640x480 LCD
- Ports: 2xUHC, 1xUDC, 1xPCMCIA, VGA, FFUART, 2xPS2, Speaker, MIC

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>