usb: Fix compile error for omaps for musb_hdrc

CONFIG_ARCH_OMAP34XX is now CONFIG_ARCH_OMAP3.

But since drivers/usb/musb/omap2430.c use CONFIG_PM for these
registers and functions, do the same for the header.

Otherwise we get the following for most omap3 defconfigs:

drivers/usb/musb/omap2430.c:261: error: expected identifier or '(' before 'do'
drivers/usb/musb/omap2430.c:261: error: expected identifier or '(' before 'while'
drivers/usb/musb/omap2430.c:268: error: expected identifier or '(' before 'do'
drivers/usb/musb/omap2430.c:268: error: expected identifier or '(' before 'while'

Signed-off-by: Tony Lindgren <tony@atomide.com>