Remove hardware dependence in portmacros.h (#1112)

Remove hardware dependence in portmacros.h (#1112)

* Remove hardware dependence in portmacros.h

The IAR MSP430X port `#include "msp430.h"` which pulls all the hardware
register definitions into anything which `#include "FreeRTOS.h"`.  This
removes that hardware dependency "leak" by removing the header file
and re-defining the `portDISABLE_INTERRUPTS()` and
`portENABLE_INTERRUPTS()` macros in terms of `__asm`.

* Code review suggestions

Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>
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Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>
Co-authored-by: Gaurav-Aggarwal-AWS <33462878+aggarg@users.noreply.github.com>
Co-authored-by: Gaurav Aggarwal <aggarg@amazon.com>