Kernel/OpenSBI: Switched to stdint.h

Not sure when I started typing cstdint but for now I want to stick to
stdint.h

kernel/drivers/opensbi/extensions/legacy.cpp

@@ -21,7 +21,7 @@ namespace opensbi::legacy {
         };
     }
 
-    SbiRet set_timer(std::uint64_t stime_value) {
+    SbiRet set_timer(uint64_t stime_value) {
 #if __riscv_xlen == 64
         return ecall(
             static_cast<sbiword_t>(ExtensionId::SET_TIMER),

kernel/drivers/opensbi/include/opensbi/opensbi.h

@@ -1,6 +1,6 @@
 #pragma once
 
-#include <cstdint>
+#include <stdint.h>
 
 namespace drivers {
 namespace opensbi {

kernel/kernel.cpp

@@ -1,5 +1,5 @@
 #include <stdarg.h>
-#include <inttypes.h>
+#include <stdint.h>
 
 #include <dtb/dtb.h>