qspi: t210: Fix QSPI clock and tap delays

When claim_bus was setting the clock, it reset the QSPI controller,
which wipes out any tap delays set by previous bootloaders (nvtboot,
CBoot for example on Nano). Instead of doing that in claim_bus, which
gets called a lot, moved clock setting to probe(), and set tap delays
there, too. Also updated clock to 80MHz to match CBoot. Now QSPI env
save works reliably again.

Signed-off-by: Tom Warren <twarren@nvidia.com>