add LPCXresso LPC1769 target

[JojoS62]

Summary of changes

This PR adds an older LPCXpresso LPC1769 target. Oldie but Goldie.
It adds also the MCU_LPC176X for modified MCU files, the existing MCU_LPC1768 is not changed.

Impact of changes

Migration actions required

Documentation

Needs updated documentation in Mbed-CE Wiki pages for this target.

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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)
[] Tests / results supplied as part of this PR

Some tests are necessary.

Todo:

• add clock options for 96 / 100 / 120 MHz
• test localfilesystem
• update Wiki pages

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[multiplemonomials]

Since LPC1769 (unlike LPC1768) can go up to 120MHz, let's increase the clock frequency if possible!

[JojoS62]

Yes, clock option is already on the todo list.

[multiplemonomials]

TODO need to update doc website