sunxi: disable Pine A64 model detection code on other boards

The Pine A64 Plus/non-Plus model detection code is now built on all
64-bit ARM SoCs, even if the code cannot be triggered when H5/H6 is in
use.

Disable them when the board is Pine A64 by adding a Kconfig option that
is only selected on Pine A64.

On GCC 7.3.1 this makes the size of the function reduces 184 bytes, and
saves a 104 byte strstr() function, then makes SPL on H6 succeed to
build.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>

arch/arm/mach-sunxi/Kconfig

@@ -970,4 +970,14 @@ config SPL_SPI_SUNXI
 	  sunxi SPI Flash. It uses the same method as the boot ROM, so does
 	  not need any extra configuration.
 
+config PINE64_DT_SELECTION
+	bool "Enable Pine64 device tree selection code"
+	depends on MACH_SUN50I
+	help
+	  The original Pine A64 and Pine A64+ are similar but different
+	  boards and can be differed by the DRAM size. Pine A64 has
+	  512MiB DRAM, and Pine A64+ has 1GiB or 2GiB. By selecting this
+	  option, the device tree selection code specific to Pine64 which
+	  utilizes the DRAM size will be enabled.
+
 endif

board/sunxi/board.c

@@ -820,6 +820,7 @@ int board_fit_config_name_match(const char *name)
 #endif
 	};
 
+#ifdef CONFIG_PINE64_DT_SELECTION
 /* Differentiate the two Pine64 board DTs by their DRAM size. */
 	if (strstr(name, "-pine64") && strstr(cmp_str, "-pine64")) {
 		if ((gd->ram_size > 512 * 1024 * 1024))
@@ -829,5 +830,7 @@ int board_fit_config_name_match(const char *name)
 	} else {
 		return strcmp(name, cmp_str);
 	}
+#endif
+	return strcmp(name, cmp_str);
 }
 #endif

configs/pine64_plus_defconfig

@@ -3,6 +3,7 @@ CONFIG_ARCH_SUNXI=y
 CONFIG_SPL=y
 CONFIG_MACH_SUN50I=y
 CONFIG_RESERVE_ALLWINNER_BOOT0_HEADER=y
+CONFIG_PINE64_DT_SELECTION=y
 CONFIG_NR_DRAM_BANKS=1
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
 # CONFIG_CMD_FLASH is not set