ppc4xx: Use common ns16550 functions in 4xx UART POST driver

This patch changes the PPC4xx POST UART driver to use the common
NS16550 functions for receiving and sending. Additionally the
local function for SoC divisor setup are removed. Instead the
functions from arch/powerpc/cpu/ppc4xx/4xx_uart.c are used. This
removes code duplication.

Also the common CONFIG_SYS_NS16550_COMx defines are now used
to describe the POST UART's.

And a compile breakage is fixed, introduced by a git merge of
the ppc4xx/next branch into master. Now "ppc4xx.h" is moved to
"asm/ppc4xx.h". Fixed as well with this patch.

Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/include/configs/zeus.h b/include/configs/zeus.h
index aa250cc..06d4526 100644
--- a/include/configs/zeus.h
+++ b/include/configs/zeus.h
@@ -94,7 +94,7 @@
 #define CONFIG_SYS_POST_ETHER_EXT_LOOPBACK	/* eth POST using ext loopack connector	*/
 
 /* Define here the base-addresses of the UARTs to test in POST */
-#define CONFIG_SYS_POST_UART_TABLE	{UART0_BASE}
+#define CONFIG_SYS_POST_UART_TABLE	{ CONFIG_SYS_NS16550_COM1 }
 
 #define CONFIG_LOGBUFFER
 #define CONFIG_SYS_POST_CACHE_ADDR	0x00800000 /* free virtual address	*/