Remove imx_clk_pllv3_locked() which was introduced for the sake of
Vybrid platform. The same effect (waiting on 'locked' bit) can be
achived with vanilla clk_pllv3_enable/disable, which make said
function unnecessary.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>