USB: EHCI: make ehci-spear a separate driver

Separate the SPEAr host controller driver from ehci-hcd host code
so that it can be built as a separate driver module.
This work is part of enabling multi-platform kernels on ARM;
however, note that other changes are still needed before SPEAr can be
booted with a multi-platform kernel, but they are queued in the
arm-soc tree for 3.10.

With the infrastructure added by Alan Stern in patch 3e023203


"USB: EHCI: prepare to make ehci-hcd a library module", we can
avoid this problem by turning a bus glue into a separate
module, as we do here for the SPEAr bus glue.

In V4 (arnd):
 - renamed all 'struct spear_ehci' pointers from 'ehci' to the
   less ambiguous 'sehci'.
 - folded trivial spear_start_ehci/spear_stop_ehci functions into
   callers.
 - brought back initialization of ehci->caps.

In V3:
 - Detailed commit message added here about why this patch is required.
 - Eliminated ehci_spear_setup routine because hcd registers can
   be directly set in the spear_ehci_hcd_drv_probe function.
 - spear_overrides struct initialized.
 - Converted to using .extra_priv_size for allocating spear_ehci,
   and updated all users of that structure.
 - to_spear_ehci() macro modified for spear_ehci.

In V2:
 - Replaced spear as SPEAr everywhere, leaving functions/variables/config options.

Signed-off-by: Deepak Saxena <dsaxena@linaro.org>
Signed-off-by: Manjunath Goudar <manjunath.goudar@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Viresh Kumar <viresh.linux@gmail.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Cc: Shiraz Hashim <shiraz.hashim@st.com>
Cc: spear-devel@list.st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>