Add PORTENTA_H7 target board

[pennam]

Summary of changes

This is a PR to add the PORTENTA_H7 target board to the mainline. I haven't tested it on hardware but I'm not getting any build error.

I've picked @facchinm commits on the arduino / mbed-os repository and manually merged few conflicts.

I've squashed all commits to make PR cleaner but if it is better i will rework it to restore commit history.

Impact of changes

All changed files are platform specific and should not impact on the system apart from:

1. connectivity/drivers/emac/TARGET_STM/stm32xx_emac.cpp -> Avoid Invalidate data cache for ETH Rx Buffers
2. connectivity/drivers/wifi/esp8266-driver/mbed_lib.json -> defined UART pins for esp8266 driver
3. connectivity/lwipstack/mbed_lib.json -> defined memory size for lwip stack
4. targets/TARGET_STM/TARGET_STM32H7/TARGET_STM32H747xI/system_clock.c -> Add WEAK attribute to allow override
5. targets/TARGET_STM/TARGET_STM32H7/objects.h -> Add qspi hal include file
6. targets/TARGET_STM/USBPhy_STM32.cpp -> Enable sleep for HS_CLOCK and HS_ULPI_CLK
7. targets/targets.json -> Add PORTENTA_H7 platform

Migration actions required

Documentation

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Pull request type

[x] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] 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

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Reviewers

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[pennam]

@facchinm after I've squashed all commits and sent the PR I thought it wasn't a great idea... so I've created another branch preserving whole commits history. Let me know wich solution do you think is better, i really don't know if it makes any difference for ARMmbed/mbed-os mantainers.

[pennam]

Closing because ARMmbed#13826 has been merged.