ARM: debug: provide 8250 debug uart register shift configuration option

Move the definition of the UART register shift out of the platform
specific header file into the Kconfig files.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mach-rpc/include/mach/debug-macro.S

@@ -18,5 +18,4 @@
 		orr	\rp, \rp, #0x03000000	@ physical
 		.endm
 
-#define UART_SHIFT	2
 #include <asm/hardware/debug-8250.S>