powerpc/microwatt: Remove unused early debug code

The original microwatt submission[1] included some early debug code for
using the Microwatt "potato" UART.

The series that was eventually merged switched to using a standard UART,
and so doesn't need any special early debug handling. But some of the
original code was merged accidentally under the non-existent
CONFIG_PPC_EARLY_DEBUG_MICROWATT.

Drop the unused code.

1: https://lore.kernel.org/linuxppc-dev/20200509050340.GD1464954@thinks.paulus.ozlabs.org/

Fixes: 48b545b8 ("powerpc/microwatt: Use standard 16550 UART for console")
Reported-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220919052755.800907-1-mpe@ellerman.id.au

arch/powerpc/kernel/udbg_16550.c

@@ -296,42 +296,3 @@ void __init udbg_init_40x_realmode(void)
 }
 
 #endif /* CONFIG_PPC_EARLY_DEBUG_40x */
-
-#ifdef CONFIG_PPC_EARLY_DEBUG_MICROWATT
-
-#define UDBG_UART_MW_ADDR	((void __iomem *)0xc0002000)
-
-static u8 udbg_uart_in_isa300_rm(unsigned int reg)
-{
-	uint64_t msr = mfmsr();
-	uint8_t  c;
-
-	mtmsr(msr & ~(MSR_EE|MSR_DR));
-	isync();
-	eieio();
-	c = __raw_rm_readb(UDBG_UART_MW_ADDR + (reg << 2));
-	mtmsr(msr);
-	isync();
-	return c;
-}
-
-static void udbg_uart_out_isa300_rm(unsigned int reg, u8 val)
-{
-	uint64_t msr = mfmsr();
-
-	mtmsr(msr & ~(MSR_EE|MSR_DR));
-	isync();
-	eieio();
-	__raw_rm_writeb(val, UDBG_UART_MW_ADDR + (reg << 2));
-	mtmsr(msr);
-	isync();
-}
-
-void __init udbg_init_debug_microwatt(void)
-{
-	udbg_uart_in = udbg_uart_in_isa300_rm;
-	udbg_uart_out = udbg_uart_out_isa300_rm;
-	udbg_use_uart();
-}
-
-#endif /* CONFIG_PPC_EARLY_DEBUG_MICROWATT */