Mbed CE support for FF_LPC546XX

[multiplemonomials]

Summary of changes

I got an L-Tek FF_LPC546XX board, and have been testing it against Mbed CE. Making some fixes and quality of life improvements so that this board can be easily used!

• Rewrite linker script to add support for memory banks, crash capture, and split heap
• Add custom MPU configuration, as the default Mbed one prevented the SRAMX bank from being written, as it was in the "code" region
• Add upload method support (MBED, PYOCD, and LINKSERVER work)
• Add component for the DataFlash chip on the board, so it works with no configuration
• Fix incorrect code (caught by a compiler warning) in the I2C slave code that likely kept I2C slave from working
• Combine duplicated override code files into one
• Fix crash reporting test (accidentally broken by Stop Greentea tests if a fatal error occurs #432)
• Remove pinmap_restricted_pins(), as it is only used for the FPGA CI test shield, which we do not have and won't be using, and it isn't implemented for most targets.
• Switch order of ROM banks in JSON so that MBED_ROM is not the EEPROM and uploading works

Impact of changes

Mbed CE now officially supports L-Tek FF_LPC546XX.

Migration actions required

Documentation

Board info page created here: https://github.com/mbed-ce/mbed-os/wiki/MCU-Info-Page:-LPC546xx

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Pull request type

[] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[X] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[X] Tests / results supplied as part of this PR

All non-skipped tests pass, except the ethernet tests, which I don't have the right ethernet jack handy to run (did order one though).

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