Change in coreboot[master]: riscv: Update the gcc built-in macro __riscv__

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Change subject: riscv: Update the gcc built-in macro __riscv__
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Patch Set 1: Verified+1

Build Successful

https://qa.coreboot.org/job/coreboot-checkpatch/10909/ : SUCCESS

https://qa.coreboot.org/job/coreboot-gerrit/55235/ : SUCCESS