ARM: imx: gpc: Initialize all power domains

Since commit 0159ec67 ("PM / Domains: Verify the PM domain is present
when adding a provider") the following regression is observed on imx6:

imx-gpc: probe of 20dc000.gpc failed with error -22

The gpc probe fails because of_genpd_add_provider_onecell() now checks
if all the domains are initialized via pm_genpd_present() function
and it fails because not all the power domains are initialized.

In order to fix this error, initialize all the power domains from
imx_gpc_domains[], not only the imx6q_pu_domain.base one.

Reported-by: Olof's autobooter <build@lixom.net>
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>