MIPS: SEAD3: Use generic ns16550a earlycon support

Stop selecting SYS_HAS_EARLY_PRINTK & remove the custom support for
early output to the ns16550a UARTs, instead relying upon generic
ns16550a earlycon support. This reduces the amount of platform code
required for SEAD3 without losing any functionality.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Jacek Anaszewski <j.anaszewski@samsung.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/14049/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -514,7 +514,6 @@ config MIPS_SEAD3
 	select SYS_HAS_CPU_MIPS32_R2
 	select SYS_HAS_CPU_MIPS32_R6
 	select SYS_HAS_CPU_MIPS64_R1
-	select SYS_HAS_EARLY_PRINTK
 	select SYS_SUPPORTS_32BIT_KERNEL
 	select SYS_SUPPORTS_64BIT_KERNEL
 	select SYS_SUPPORTS_BIG_ENDIAN