aarch64: Add ILP32 support.

Instead of setting a fix value of 48 allowed VA bits,
we distiguish between LP64 and ILP32.

Testsuite result with LP64:
Test suite summary: pass: 13/13, skip: 0/13, fail: 0/13

Testsuit result with ILP32:
Test suite summary: pass: 13/13, skip: 0/13, fail: 0/13

Signed-off-by: Christoph Muellner <christoph.muellner@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>