ARM: pxa: export symbols from pxa3xx-ulpi

The pxa3xx_u2d_start_hc/pxa3xx_u2d_stop_hc symbols are used by the
ohci-pxa27x driver, which can be a module.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>