Revert "MIPS: Add custom serial.h with BASE_BAUD override for generic kernel"

This reverts commit c8ec2041f5.

There's no more need to set BASE_BAUD to 0 to make earlycon work
properly on DTS-based boards since such cases were handled in commit
182ead3e41 ("earlycon: Remove hardcoded port->uartclk initialization
in of_setup_earlycon"). earlycon no longer initializes port->uartclk
with a value of BASE_BAUD * 16 when starting from FDT/OF.

Signed-off-by: Alexander Lobakin <alobakin@dlink.ru>
Signed-off-by: Paul Burton <paulburton@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Microchip Linux Driver Support <UNGLinuxDriver@microchip.com>
Cc: Will Deacon <will@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Allison Randal <allison@lohutok.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

arch/mips/include/asm/Kbuild

@@ -19,6 +19,7 @@ generic-y += preempt.h
 generic-y += qrwlock.h
 generic-y += qspinlock.h
 generic-y += sections.h
+generic-y += serial.h
 generic-y += trace_clock.h
 generic-y += unaligned.h
 generic-y += user.h

arch/mips/include/asm/serial.h

@@ -1,18 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-or-later */
-/*
- * Copyright (C) 2017 MIPS Tech, LLC
- */
-#ifndef __ASM__SERIAL_H
-#define __ASM__SERIAL_H
-
-#ifdef CONFIG_MIPS_GENERIC
-/*
- * Generic kernels cannot know a correct value for all platforms at
- * compile time. Set it to 0 to prevent 8250_early using it
- */
-#define BASE_BAUD 0
-#else
-#include <asm-generic/serial.h>
-#endif
-
-#endif /* __ASM__SERIAL_H */