soc/core: Add reset latches

soc/core: Add reset latches

This adds one-cycle latches to the various resets out of the soc and
into the various core modules. It *seems* to help vivado P&R a bit
and has shown to avoid timing violations under some circumstances.

Interestingly those resets never seem to appear in the bad timing
path. It looks like those long resets simply impose placement
constraints that Vivado satisfies at the expense of timing elsewhere.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>