clk: davinci: New driver for davinci PSC clocks

This adds a new driver for mach-davinci PSC clocks. This is porting the
code from arch/arm/mach-davinci/psc.c to the common clock framework and
is converting it to use regmap to simplify the code. Additionally, it
adds device tree support for these clocks.

Note: although there are similar clocks for TI Keystone we are not able
to share the code for a few reasons. The keystone clocks are device tree
only and use legacy one-node-per-clock bindings. Also the keystone
driver makes the assumption that there is only one PSC per SoC and uses
global variables, but here we have two controllers per SoC.

Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>