ARM: imx: imx8m: Introduce and use UART_BASE_ADDR(n)

Introduce helper macro UART_BASE_ADDR(n), which returns Nth UART base
address. Convert all board configurations to this new macro. This is the
first step toward switching CONFIG_MXC_UART_BASE to Kconfig. This is a
clean up, no functional change.

The new macro contains compile-time test to verify N is in suitable
range. The test works such that it multiplies constant N by constant
double-negation of size of a non-empty structure, i.e. it multiplies
constant N by constant 1 in each successful compilation case.

The non-empty structure may contain C11 _Static_assert(), make use of
this and place the kernel variant of static assert in there, so that
it performs the compile-time check for N in the correct range. Note
that it is not possible to directly use static_assert in compound
statements, hence this convoluted construct.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <festevam@denx.de>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>

arch/arm/include/asm/arch-imx8m/imx-regs.h

@@ -48,6 +48,16 @@
 #ifdef CONFIG_IMX8MM
 #define USDHC3_BASE_ADDR	0x30B60000
 #endif
+#define UART_BASE_ADDR(n)	(			\
+	!!sizeof(struct {				\
+		static_assert((n) >= 1 && (n) <= 4);	\
+		int pad;				\
+		}) * (					\
+	(n) == 1 ? UART1_BASE_ADDR :			\
+	(n) == 2 ? UART2_BASE_ADDR :			\
+	(n) == 3 ? UART3_BASE_ADDR :			\
+	UART4_BASE_ADDR)				\
+	)
 
 #define TZASC_BASE_ADDR		0x32F80000