Change in coreboot[master]: Simplify the code of riscv exception handling

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Change subject: Simplify the code of riscv exception handling
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Patch Set 1: Verified+1

Build Successful

https://qa.coreboot.org/job/coreboot-checkpatch/10605/ : SUCCESS

https://qa.coreboot.org/job/coreboot-gerrit/54908/ : SUCCESS