Fix nrf internal flash

[tannewt]

nRF internal flash didn't fake out the partition table like atmel does. Now its factored out.

[jerryneedell]

built and tested on pca10059 (nrf52840 dongle) and on feather_nrf52832
Both appear to work normally.
It takes about 10 seconds or so for REPL to appear on pca10059 -- got nervous ;-)
On feather_nrf52832 if SPI is used then a soft RESET (control-D) is issued another attempt to use SPI results inc"SCK in use" error. A Hard RESET clears the condition and it works as expected.
Tested ampy access to feather_nrf52832 -- tried ls,get,put -- all ok

also tested on pca10056 (nrf52840 DK) looks good.

[dhalbert]

If the delayed REPL is consistent, then an issue should be opened. It might have been a long write to BOOT_OUT.TXT (because the version changed).

[dhalbert]

I see the slow REPL response as well. CIRCUITPY is almost immediate. I can connect to the serial port immediately, but it takes about 7 seconds for the REPL prompt to show up. This is true after multiple resets (it's not just the first one, which might write BOOT_OUT.txt). I'l make an issue with some more data.