ARM: DRA7: Fixup DSPEVE, IVA and GPU clock frequencies based on OPP

This patch adds support to update the device-tree blob to adjust the
DSP and IVA DPLL clocks pertinent to the selected OPP choice, with
the default being OPP_NOM. The voltage settings are done in u-boot,
but the actual clock configuration itself is done in kernel because
of the following reasons:
1. SoC definition constraints us to NOT to do dynamic voltage
   scaling ever after the initial avs0 setting in bootloader
   - so the voltage must be set in bootloader.
2. The voltage level must be set even if the IP blocks like
   GPU/DSP are unused.
3. The IVA, GPU and DSP DPLLs are not essential for u-boot functionality,
   and similar DPLL clock configuration code has been cleaned up in
   v2014.10 u-boot release. See commit, 02c41535 ("ARM: OMAP4/5:
   Remove dead code against CONFIG_SYS_CLOCKS_ENABLE_ALL").

The non-essential DPLLs are configured within the kernel during
the clock init step when parsing the device tree and creating
the clock devices. This approach meets both the u-boot and kernel
needs.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Subhajit Paul <subhajit_paul@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>