ARM: tegra: only build __pinmux_nand() when it's needed

__pinmux_nand() won't compile if PERIPH_ID_NDFLASH isn't defined.
Prevent this from causing build problems on newer SoCs without NAND
support (or without SW support for NAND yet), but preventing
compilation unless the function will actually be used, i.e. when
CONFIG_TEGRA_NAND is defined.

Signed-off-by: Tom Warren <twarren@nvidia.com>
[swarren, rewrote commit description, moved ifdef around whole function
rather than just body]
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>

board/nvidia/common/board.c

@@ -67,12 +67,14 @@ void __gpio_early_init_uart(void)
 void gpio_early_init_uart(void)
 __attribute__((weak, alias("__gpio_early_init_uart")));
 
+#if defined(CONFIG_TEGRA_NAND)
 void __pin_mux_nand(void)
 {
 	funcmux_select(PERIPH_ID_NDFLASH, FUNCMUX_DEFAULT);
 }
 
 void pin_mux_nand(void) __attribute__((weak, alias("__pin_mux_nand")));
+#endif
 
 void __pin_mux_display(void)
 {