ARM: imx27: clk-imx27: SPI: Rename IPG clock and add PER clock

spi-imx driver needs two clock: ipg and per. The first clock must be named and
the second must be added.

Signed-off-by: Gwenhael Goavec-Merou <gwenhael.goavec-merou@armadeus.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>