Dev hf illegal instr test update

Created by: silabs-hfegran

Updated illegal_instr_test to be able to handle bitmanip extensions present/not present

Summary of changes:

• Gatheres all bitmanip instructions present in the original test into one function (test_bitmanip)
• Housekeeping to keep registers in a sane state
• A few bitmanip-instructions were modified to avoid stack pointer corruption
• Sets a register to a55a5aa5 if all bitmanip instructions pass as valid instructions - this value is used as a flag to signal bitmanip support.
• Evaluates if the amount of invalid instructions matches the expected value (this value differs by 77 depending on if bitmanip support is enabled or not). Signed-off-by: Henrik Fegran Henrik.Fegran@silabs.com