ARM: davinci: psc: fix incorrect offsets

Seperate PDSTAT and PDCTL registers are defined for
domain 0 and domain 1 where as the code always reads
the domain 0 PDSTAT register and domain 1 PDCTL register.

Fix this issue. While at it, introduce usage of macros
for register masks to improve readability.

Reviewed-by: Sergei Shtylyov <sshtylyov@mvista.com>
Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>