[media] atmel-isi: add code to enable/disable ISI_MCK clock

This patch
- add ISI_MCK clock enable/disable code.
- change field name in isi_platform_data structure

Signed-off-by: Josh Wu <josh.wu@atmel.com>
[g.liakhovetski@gmx.de: fix label names]
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>