mpc85xx: add SPI kernel loader for TP-Link TL-WDR4900 v1

Similar to the lzma-loader on our MIPS targets, the spi-loader acts as
a second-stage loader that will then load and start the actual kernel.
As the TL-WDR4900 uses SPI-NOR and the P1010 family does not have support
for memory mapping of this type of flash, this loader needs to contain a
basic driver for the FSL ESPI controller.

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
(cherry picked from commit a296055b82)

target/linux/mpc85xx/image/spi-loader/include/stdio.h

@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: BSD-2-Clause
+/*
+ * Copyright (c) 2022 Matthias Schiffer <mschiffer@universe-factory.net>
+ */
+
+#pragma once
+
+#include <serial.h>
+#include <types.h>
+
+static inline int getchar(void)
+{
+	return serial_console_getchar();
+}
+
+static inline int tstc(void)
+{
+	return serial_console_tstc();
+}
+
+static inline int putchar(char c)
+{
+	if (c == '\n')
+		serial_console_putchar('\r');
+	serial_console_putchar(c);
+	return 0;
+}
+
+int puts(const char *s);
+
+/* Utility functions */
+void put_u4(uint8_t v);
+void put_u8(uint8_t v);
+void put_u16(uint16_t v);
+void put_u32(uint32_t v);
+void put_ptr(const void *p);
+void put_array(const void *p, size_t l);
+
+#define put_with_label(label, put, value) do { \
+		puts(label); \
+		put(value); \
+		puts("\n"); \
+	} while (0)