microblaze: switch to 2.28, make pr21017 patch musl specific

target/config/Config.in.binutils

@@ -6,7 +6,6 @@ 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_2_26_1 if ADK_TARGET_ARCH_MICROBLAZE
 default ADK_TOOLCHAIN_BINUTILS_2_28
 
 config ADK_TOOLCHAIN_BINUTILS_GIT