PXA: fix environment sector size, kernel and environment location for vpac270

Define ENV_ADDR as MONITOR_BASE + MONITOR_LEN. Fix environment sector
size (NOR: 32Kb for first four sectors and 128Kb for other; OneNAND: 128Kb).

Last but not least: we have MONITOR_LEN = 0x40000 and one sector for
environment (size = 0x20000), so the kernel may start from 0x00060000 only.

Signed-off-by: Mikhail Kshevetskiy <mikhail.kshevetskiy@gmail.com>