TOSA: Support for TABLE operator (int8)

Added support to map TABLE operator to LUT.
Limitations:
-Only supported for int8
-TABLE input must be constant

This also adds the support for TFLite legalisation of
Tanh/Sigmoid (int8/uint8).

Signed-off-by: Patrik Gustavsson <patrik.gustavsson@arm.com>
Change-Id: I1a95f61fb02fdd42c4a690494418cc0765c8b275