MLK-16101 MU: avoid read mu version register every scu call

MLK-16101 MU: avoid read mu version register every scu call

Generally read mu registers will take about 225ns.
Overall scu_clk_enable function takes about 8000ns to 150000ns.
Although read version register just take 3% time,
it is not necessary to read version register every time.

Signed-off-by: Frank Li <Frank.Li@nxp.com>