This provides an alternative esp32-specific SPI driver with ops that can be
swapped in place of the gpio bitbang one.
The pinmux info and lws gpio driver and other data in the spi bitbang
struct are used as-is by the DMA one.
New ops are provided which are able to allocate and free DMA-able memory so
the device drivers can prepare directly usable buffers. Bounce through to
DMA-able buffers is also transparently supported.
Add lws_display and minimal example support for esp32-wrover to match wsp32-heltec-wb32
Since no usable buttons that don't affect something else on wrover kit, assumes
a button to 0V on GPIO14.