MTVEC interrupt vector default value

Created by: silabs-PaulZ

The default value of the MTVEC, interrupt and exception vector address, is set to 0. If an exception occurs before SW has reconfigured MTVEC to the proper location then the processor will be in a deadlock situation.

We should add the mtvec_addr_i port, similar to boot_addr_i, that defines the default value of the MTVEC CSR value. This allows the user to customize the default boot and MTVEC locations together. MTVEC will still adhere to the specification where it can be changed via a CSR write.