lib: Create a separate math helper function file

There may be few common mathematics helper functions which can be used
anywhere in OpenSBI project.

Add a separate math helper function file to add these functions.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>

lib/sbi/sbi_math.c

@@ -0,0 +1,23 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2020 Western Digital Corporation or its affiliates.
+ *
+ * Common helper functions used across OpenSBI project.
+ *
+ * Authors:
+ *   Atish Patra <atish.patra@wdc.com>
+ */
+
+unsigned long log2roundup(unsigned long x)
+{
+	unsigned long ret = 0;
+
+	while (ret < __riscv_xlen) {
+		if (x <= (1UL << ret))
+			break;
+		ret++;
+	}
+
+	return ret;
+}