musl: use binutils git for mips, because of a regression in 2.28

target/config/Config.in.binutils

@@ -6,6 +6,7 @@ prompt "Binutils version"
 default ADK_TOOLCHAIN_BINUTILS_ARC if ADK_TARGET_ARCH_ARC
 default ADK_TOOLCHAIN_BINUTILS_NDS32 if ADK_TARGET_ARCH_NDS32
 default ADK_TOOLCHAIN_BINUTILS_2_20_1 if ADK_TARGET_ARCH_AVR32
+default ADK_TOOLCHAIN_BINUTILS_GIT if ADK_TARGET_ARCH_MIPS && ADK_TARGET_LIB_MUSL
 default ADK_TOOLCHAIN_BINUTILS_2_28
 
 config ADK_TOOLCHAIN_BINUTILS_GIT