x86: Add missing kernel option CONFIG_X86_DECODER_SELFTEST

This option has now a different dependency and can be activated, set a
default value.

Fixes: 20b5a4ca ("kernel: bump 4.19 to 4.19.101")
Signed-off-by: Hauke Mehrtens <hauke.mehrtens@intel.com>
Tested-by: Alexandru Ardelean <ardeleanalex@gmail.com>

target/linux/x86/config-4.14

@@ -469,6 +469,7 @@ CONFIG_X86_CMPXCHG64=y
 # CONFIG_X86_CPUFREQ_NFORCE2 is not set
 # CONFIG_X86_CPUID is not set
 # CONFIG_X86_DEBUG_FPU is not set
+# CONFIG_X86_DECODER_SELFTEST is not set
 # CONFIG_X86_EXTENDED_PLATFORM is not set
 CONFIG_X86_F00F_BUG=y
 CONFIG_X86_FAST_FEATURE_TESTS=y

target/linux/x86/config-4.19

@@ -453,6 +453,7 @@ CONFIG_X86_CMPXCHG64=y
 # CONFIG_X86_CPUFREQ_NFORCE2 is not set
 # CONFIG_X86_CPUID is not set
 # CONFIG_X86_DEBUG_FPU is not set
+# CONFIG_X86_DECODER_SELFTEST is not set
 # CONFIG_X86_EXTENDED_PLATFORM is not set
 CONFIG_X86_F00F_BUG=y
 CONFIG_X86_FEATURE_NAMES=y