Fix IAR alignment issues if __packed has been redefined into a macro.

[LoveKarlsson]

Description

While porting Zephyr to work with IAR tools, a problem was discovered
due to Zephyr defining a macro, __packed, the overrides the IAR keyword
__packed.

The macro is defined to attribute(packed) in Zephyr.

As Zephyr uses mbedtls as an external module, the macro __packed that
Zephyr sets up does not work with the typedefs of unaligned int
types in core/alignment.h.

We therefor save the macro (if set), undefine it, declare the unaligned int types,
and restore the macro afterwards.

When accepted, a backport to the version Zephyr uses will be made.

PR checklist

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• changelog not required because: change does not affect generated code in normal use with IAR tools
• framework PR not required
• mbedtls PR not required
• tests not required because: no functionality has been changed