OMAP2/3 clockdomains: combine pwrdm, pwrdm_name into union in struct clockdomain

struct clockdomain contains a struct powerdomain *pwrdm and const char
*pwrdm_name.  The pwrdm_name is only used at initialization to look up
the appropriate pwrdm pointer.  Combining these into a union saves
about 100 bytes on 3430SDP.  This patch should not cause any change in
kernel function.

Boot-tested on 3430SDP ES2.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
size:
   text    data     bss     dec     hex filename
3391587  157104  107136 3655827  37c893 vmlinux.3430sdp.orig
3391555  157032  107136 3655723  37c82b vmlinux.3430sdp
Signed-off-by: Tony Lindgren <tony@atomide.com>