ARM: OMAP4: hwmod: rename _enable_module to _omap4_enable_module()

_enable_module is specific to SoCs with PRCM interfaces similar to
that of the OMAP4, so rename it to be consistent with the
corresponding _omap4_disable_module.

Signed-off-by: Kevin Hilman <khilman@ti.com>
[paul@pwsan.com: tweaked commit message]
Signed-off-by: Paul Walmsley <paul@pwsan.com>