x86/legacy: fix subtarget CPU for kernel 5.10

The 5.10 target config defined a baseline i686 CPU aligned to the 32-bit
generic subtarget. However, the legacy subtarget arch wasn't set to the
older 586MMX, defaulting instead to the i686.

Explicitly set the subtarget arch and refresh the subtarget config, as done
already with the old geode subtarget.

Fixes: 8391781389 ("x86: support kernel 5.10")
Signed-off-by: Tony Ambardar <[email protected]>

target/linux/x86/legacy/config-5.10

@@ -140,6 +140,8 @@ CONFIG_ISO9660_FS=y
 # CONFIG_JOLIET is not set
 CONFIG_KCMP=y
 # CONFIG_LANCE is not set
+CONFIG_M586MMX=y
+# CONFIG_M686 is not set
 # CONFIG_MDA_CONSOLE is not set
 CONFIG_MFD_CORE=y
 CONFIG_MFD_INTEL_LPSS=y
@@ -201,11 +203,14 @@ CONFIG_VMAP_PFN=y
 # CONFIG_WDT is not set
 CONFIG_X86_ACPI_CPUFREQ=y
 # CONFIG_X86_ACPI_CPUFREQ_CPB is not set
+CONFIG_X86_ALIGNMENT_16=y
 # CONFIG_X86_AMD_FREQ_SENSITIVITY is not set
 # CONFIG_X86_AMD_PLATFORM_DEVICE is not set
 # CONFIG_X86_E_POWERSAVER is not set
+CONFIG_X86_F00F_BUG=y
 # CONFIG_X86_INTEL_LPSS is not set
 # CONFIG_X86_LONGHAUL is not set
+CONFIG_X86_MINIMUM_CPU_FAMILY=5
 # CONFIG_X86_PAE is not set
 # CONFIG_X86_PCC_CPUFREQ is not set
 CONFIG_X86_PM_TIMER=y