Update rtos_qspi_flash driver to use "xmos_flash"

[keithm-xmos]

Most should be straight forward. The safety of rtos_qspi_flash_read_ll() needs to be evaluated once implementation is in, but it appears safe from quick glance.

Functional benchmarking and verification at application level: This change may break:

sln_voice/ffd (high)
sln_voice/stlp (low)
xcore_sdk/examples/freertos/usb (med)
xcore_sdk/examples/freertos/iot (med)
xcore_sdk/examples/freertos/explorer_board (low)
xcore_sdk/examples/freertos/l2_cache (low)
xcore_sdk/examples/bare-metal/explorer_board (low)

Add driver support and docs for manual flash parameters. Will reference:
https://www.xmos.ai/documentation/XM-014363-PC-LATEST/html/tools-guide/tutorials/add-flash-support/flash.html

Update tests for added/removed features. This work should include #101

See xmos/xcore_iot#501

[xmos-jmccarthy]

Driver updated and verified with #101.

Tools API update requests can be found in: Bug 18717

Update could not be done backwards compatible, so PR will be on hold until XTC 15.2.0 is public, as this tools version will be the required minimum version.

[xmos-jmccarthy]

https://github.com/xmos/fwk_rtos/tree/feature/tools_qspi_lib
Passes tests with sdk:
https://github.com/xmos/xcore_sdk/tree/feature/tools_qspi_lib

Blocked until public Tools 15.2.0 release.

[xmos-jmccarthy]

Due to performance of lib_quadflash, this issue will be changed to update rtos_qspi_flash_driver to use xmos_flash instead.

[keithm-xmos]

Changed name. Also note that this requires XTC 15.2.

[keithm-xmos]

Change name again to reflect current plan of using libquadflash and lib_fast_flash_read

• Remove qspi_io
• Add lib_fast_flash_read
• Update RTOS driver for lib_quadflash and lib_fast_flash_read usage

Closed duplicate task #128