64KB block and chip erase for Nordic nrf52 QSPI
64KB block and chip erase for Nordic nrf52 QSPI

Without a hff_erase implementation for HAL flash functions,
the HAL flash layer will default to sector erase for all
erase functions, regardless of length.

This change implements hff_erase, and will issue a chip erase
or 64KB block erase where possible based on the address and
length of area to be erased.

On the nRF52840 DK (PCA10056) using the provided MX25R6435F QSPI
flash, I measured a 4K sector erase of about 84 mS.  With this
patch, a 64KB block erase averages about 1164 mS.  This saves
about 176 mS per 64K erase.

mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core