[RISCV] Deduplicate version struct in RISCVISAInfo. NFC (#77645)

We have two structs for representing the version of an extension in
RISCVISAInfo, RISCVExtensionInfo and RISCVExtensionVersion, both
with the exact same fields. This patch deduplicates them.

GitOrigin-RevId: 79889fedc57707e99740abc1f48e6c5601d5a3f3
diff --git a/ELF/Arch/RISCV.cpp b/ELF/Arch/RISCV.cpp
index 62498de..8906de0 100644
--- a/ELF/Arch/RISCV.cpp
+++ b/ELF/Arch/RISCV.cpp
@@ -957,8 +957,8 @@
   } else {
     for (const auto &ext : info.getExtensions()) {
       if (auto it = mergedExts.find(ext.first); it != mergedExts.end()) {
-        if (std::tie(it->second.MajorVersion, it->second.MinorVersion) >=
-            std::tie(ext.second.MajorVersion, ext.second.MinorVersion))
+        if (std::tie(it->second.Major, it->second.Minor) >=
+            std::tie(ext.second.Major, ext.second.Minor))
           continue;
       }
       mergedExts[ext.first] = ext.second;