Fix#45-afonly+icepll+69Mhz -- for testing.

[RGD2]

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Builds on the latter, with the j1a core clock increased to 69 MHz. This appears to work -- but probably needs more extensive testing. There don't appear to be any convenient steps between 48 MHz and 69 MHz.

[RGD2]

Probably shouldn't be pulled unless we can confirm with perhaps icetime + OpenTimer that it is reasonable.