misc: aspeed-lpc: Request and enable LPC clock

The LPC device needs to ensure it's clock is enabled before it can do
anything.

In the past the clock was enabled and left running by u-boot, however
Linux now has an upstream clock driver that disables unused clocks.

Tested-by: Lei YU <mine260309@gmail.com>
Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Cyril Bur <cyrilbur@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>