efi_loader: add efi_create_indexed_name()

This function will be used from several places in UEFI subsystem
to generate some specific form of utf-16 variable name.
For example, L"Capsule0001"

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Move function to separate module.
Use char * as argument instead of u16 *.
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

lib/efi_loader/efi_string.c

@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * String functions
+ *
+ * Copyright (c) 2020 AKASHI Takahiro, Linaro Limited
+ */
+
+#include <common.h>
+#include <charset.h>
+
+/**
+ * efi_create_indexed_name - create a string name with an index
+ * @buffer:	Buffer
+ * @name:	Name string
+ * @index:	Index
+ *
+ * Create a utf-16 string with @name, appending @index.
+ * For example, L"Capsule0001"
+ *
+ * The caller must ensure that the buffer has enough space for the resulting
+ * string including the trailing L'\0'.
+ *
+ * Return: A pointer to the next position after the created string
+ *	   in @buffer, or NULL otherwise
+ */
+u16 *efi_create_indexed_name(u16 *buffer, const char *name, unsigned int index)
+{
+	u16 *p = buffer;
+	char index_buf[5];
+
+	utf8_utf16_strcpy(&p, name);
+	sprintf(index_buf, "%04X", index);
+	utf8_utf16_strcpy(&p, index_buf);
+
+	return p;
+}