vexpress64: remove #error

This patch allows vexpress64 targets to be compiled when
CONFIG_SYS_FLASH_CFI is enabled.

I considered using #warning instead of #error, but this just clutters up
the build output and hides real warnings.

Without this patch, you see errors during compilation like this:

include/configs/vexpress_aemv8a.h:42:2: error: #error "Unknown board
variant"
 #error "Unknown board variant"
include/configs/vexpress_aemv8a.h:115:2: error: #error "Unknown board
variant"
 #error "Unknown board variant"
include/configs/vexpress_aemv8a.h:280:2: error: #error "Unknown board
variant"
 #error "Unknown board variant"
make[1]: *** [tools/envcrc.o] Error 1
make: *** [tools] Error 2
In file included from include/config.h:5:0,
                 from tools/envcrc.c:19:

Signed-off-by: Ryan Harkin <ryan.harkin@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>

include/configs/vexpress_aemv8a.h

@@ -35,8 +35,6 @@
 #elif CONFIG_TARGET_VEXPRESS64_JUNO
 #define CONFIG_SYS_TEXT_BASE		0xe0000000
 #define CONFIG_SYS_INIT_SP_ADDR         (CONFIG_SYS_SDRAM_BASE + 0x7fff0)
-#else
-#error "Unknown board variant"
 #endif
 
 #define CONFIG_SYS_BOOTM_LEN (64 << 20)      /* Increase max gunzip size */
@@ -108,8 +106,6 @@
 #elif CONFIG_TARGET_VEXPRESS64_JUNO
 #define GICD_BASE			(0x2C010000)
 #define GICC_BASE			(0x2C02f000)
-#else
-#error "Unknown board variant"
 #endif
 #endif /* !CONFIG_GICV3 */
 
@@ -278,8 +274,6 @@
 
 #define CONFIG_BOOTDELAY		1
 
-#else
-#error "Unknown board variant"
 #endif
 
 /* Do not preserve environment */