ARM: 6930/1: SPEAr3xx: Rework pmx_dev code to remove conflicts

Prefix the pmx_devs to remove naming conflicts between the three
SPEAr3xx platforms. Also make pmx_driver static to each platform and
rework the init code to pass the devices rather than export the
pmx_driver structure.

Reviewed-by: Stanley Miao <stanley.miao@windriver.com>
Signed-off-by: Ryan Mallon <ryan@bluewatersys.com>
Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>