ARM: OMAP3: PM: Remove IO Daisychain control from cpuidle

As IO Daisy chain sequence is triggered via hwmod mux, there is no need to
control it from cpuidle path for OMAP3.

Also as omap3_disable_io_chain is no longer being used, just remove the
function.

Signed-off-by: Vishwanath BS <vishwanath.bs@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>
Reviewed-by: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>