Increase SPIDEV buffer size to 128k on pi0 board

[newtonick]

See SeedSigner/seedsigner#420

TLDR: provides modest performance gain when refreshing the display

[jdlcdl]

I used your changes for pi0 and pi0-dev for pi2 and pi2-dev (which are still needed).

I already had a container built for pi2-dev so I built with no-clean and used ss's latest pr420 at 32eda52.

This pr by itself is noticeably faster. (ack as soon as other boards are updated, but pi2 works great).

[newtonick]

Do we want this update in other boards without addressing frame rate and button hold timing concerns?

My thought was to do other boards in a separate PR.

[jdlcdl]

I'll get a pi0 container going.

Now that I have a pi0 container again.

ACK tested

...on pi0 using ss's latest pr420 at 32eda52
...and at 327662 with fps at 6. Now it feels like a pi2. I got 6.05 fps when I enabled show_framerate in scan_screens. And the screensaver looks a bit nervous/anxious/hyper, but much smoother