[ARM] ohci-pxa27x: introduce flags to avoid direct access to OHCI registers

Direct access to USB host controller registers is considered to be not
portable, and is usually a bad sign for poorly abstracted interface.
Introduce .flags and .power_on_delay to "struct pxaohci_platform_data"
so that most platforms don't bother to write their own .init/.exit()
sequences.

Signed-off-by: Eric Miao <eric.miao@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>