arc: use more universal prefix for default CROSS_COMPILE

As doc/README.ARC says, pre-build ARC toolchains are available at
the Synopsys GitHub page.

The bin files are prefixed with arc(eb)-buildroot-linux- for earlier
releases, but with arc(eb)-snps-linux- for the latest releases.

The symbolic links prefixed with arc(eb)-linux- are also available
for all the release, so those prefixes can be used as the default
CROSS_COMPILE regardless of the toolchains version/variants.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

arch/arc/config.mk

@@ -11,13 +11,13 @@ CONFIG_SYS_BIG_ENDIAN = 1
 endif
 
 ifdef CONFIG_SYS_LITTLE_ENDIAN
-ARC_CROSS_COMPILE := arc-buildroot-linux-uclibc-
+ARC_CROSS_COMPILE := arc-linux-
 PLATFORM_LDFLAGS += -EL
 PLATFORM_CPPFLAGS += -mlittle-endian
 endif
 
 ifdef CONFIG_SYS_BIG_ENDIAN
-ARC_CROSS_COMPILE := arceb-buildroot-linux-uclibc-
+ARC_CROSS_COMPILE := arceb-linux-
 PLATFORM_LDFLAGS += -EB
 PLATFORM_CPPFLAGS += -mbig-endian
 endif