Instead of using hard coded clock increment values for each SoC derive
the clock increment from the module clock. This is done in preparation
to support a second platform, R-Car V4H that uses a 200Mhz clock
compared with the 320Mhz clock used on R-Car S4.

Tested on both SoCs,

S4 reports a clock of 320000000Hz which gives a value of 0x19000000.
Documentation says a 320Mhz clock is used and the correct increment for
that clock is 0x19000000.

V4H reports a clock of 199999992Hz which gives a value of 0x2800001a.
Documentation says a 200Mhz clock is used and the correct increment for
that clock is 0x28000000.
Suggested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>