OMAP4: powerdomain: Add pwrdm_clear_all_prev_pwrst

Like OMAP3, OMAP4430 ES2 has additional bitfields in PWRSTST register
which help identify the previous power state entered by the
powerdomain.  Add pwrdm_clear_all_prev_pwrst to the OMAP4 powerdomains
implementation to support this.

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Rajendra Nayak <rnayak@ti.com>
[paul@pwsan.com: clarified commit message]
Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Benoit Cousson <b-cousson@ti.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Reviewed-by: Kevin Hilman <khilman@deeprootsystems.com>
Tested-by: Kevin Hilman <khilman@deeprootsystems.com>
Tested-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Tested-by: Rajendra Nayak <rnayak@ti.com>