armv8.1-m: Remove portHAS_PACBTI_FEATURE macro (#1192)

armv8.1-m: Remove portHAS_PACBTI_FEATURE macro (#1192)

The PACBTI is an optional hardware security feature,
the current implementation assumes that every SoC that
has Armv8.1-M architecture extension, has the PACBTI
hardware feature, which does not have to be the case.
Hence, the `portHAS_PACBTI_FEATURE` is removed
and the implementation is modified to rely on
`configENABLE_PAC` and `configENABLE_BTI` macros
that can either be set using CMake or FreeRTOSConfig.h
header file.

Enabling PAC and/or BTI on a port variant that
doesn't have the PACBTI hardware feature would be
caught by a `configASSERT` statement.

Signed-off-by: Ahmed Ismail <Ahmed.Ismail@arm.com>
Co-authored-by: Tony Josi <tonyjosi@amazon.com>