x86: enable 4G high memory support for generic (32bit) subtarget

This is required to fully support a number of 32bit x86 systems equipped
with more than one GB ram, e.g. certain Atom CPU machines.

Ref: https://forum.lede-project.org/t/17-01-1-x86-doesnt-detect-all-of-the-ram/3295

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

target/linux/x86/config-4.9

@@ -9,6 +9,7 @@ CONFIG_AMD_NB=y
 CONFIG_ARCH_CLOCKSOURCE_DATA=y
 CONFIG_ARCH_DEFCONFIG="arch/x86/configs/i386_defconfig"
 CONFIG_ARCH_DISCARD_MEMBLOCK=y
+CONFIG_ARCH_ENABLE_MEMORY_HOTPLUG=y
 CONFIG_ARCH_HAS_CACHE_LINE_SIZE=y
 CONFIG_ARCH_HAS_CPU_RELAX=y
 CONFIG_ARCH_HAS_ELF_RANDOMIZE=y
@@ -210,7 +211,9 @@ CONFIG_HAVE_SYSCALL_TRACEPOINTS=y
 CONFIG_HAVE_UID16=y
 CONFIG_HAVE_UNSTABLE_SCHED_CLOCK=y
 CONFIG_HAVE_USER_RETURN_NOTIFIER=y
-# CONFIG_HIGHMEM4G is not set
+CONFIG_HIGHMEM=y
+CONFIG_HIGHMEM4G=y
+# CONFIG_HIGHPTE is not set
 CONFIG_HPET_EMULATE_RTC=y
 CONFIG_HPET_TIMER=y
 # CONFIG_HP_WATCHDOG is not set
@@ -302,7 +305,7 @@ CONFIG_NEED_SG_DMA_LENGTH=y
 # CONFIG_NET5501 is not set
 # CONFIG_NET_NS is not set
 CONFIG_NLS=y
-CONFIG_NOHIGHMEM=y
+# CONFIG_NOHIGHMEM is not set
 CONFIG_NO_BOOTMEM=y
 CONFIG_NR_CPUS=1
 # CONFIG_NSC_GPIO is not set
@@ -345,7 +348,6 @@ CONFIG_PROC_PAGE_MONITOR=y
 # CONFIG_RCU_STALL_COMMON is not set
 CONFIG_RD_BZIP2=y
 CONFIG_RD_GZIP=y
-# CONFIG_RELOCATABLE is not set
 CONFIG_RTC_CLASS=y
 CONFIG_RTC_MC146818_LIB=y
 CONFIG_RWSEM_XCHGADD_ALGORITHM=y
@@ -432,7 +434,6 @@ CONFIG_X86_MINIMUM_CPU_FAMILY=4
 CONFIG_X86_MPPARSE=y
 CONFIG_X86_MSR=y
 # CONFIG_X86_P4_CLOCKMOD is not set
-# CONFIG_X86_PAE is not set
 CONFIG_X86_PAT=y
 CONFIG_X86_PLATFORM_DEVICES=y
 # CONFIG_X86_POWERNOW_K6 is not set

target/linux/x86/legacy/config-default

@@ -120,6 +120,7 @@ CONFIG_HAVE_CLK_PREPARE=y
 CONFIG_HDMI=y
 CONFIG_HID=y
 CONFIG_HID_BATTERY_STRENGTH=y
+# CONFIG_HIGHMEM4G is not set
 CONFIG_HPET=y
 CONFIG_HPET_MMAP=y
 # CONFIG_HP_ACCEL is not set
@@ -169,6 +170,7 @@ CONFIG_MOUSE_PS2_SYNAPTICS=y
 CONFIG_MOUSE_PS2_TRACKPOINT=y
 # CONFIG_MOUSE_SERIAL is not set
 # CONFIG_MOUSE_VSXXXAA is not set
+CONFIG_NOHIGHMEM=y
 CONFIG_NO_HZ=y
 CONFIG_PATA_AMD=y
 CONFIG_PATA_ATIIXP=y
@@ -217,6 +219,7 @@ CONFIG_X86_ACPI_CPUFREQ=y
 # CONFIG_X86_E_POWERSAVER is not set
 # CONFIG_X86_INTEL_LPSS is not set
 # CONFIG_X86_LONGHAUL is not set
+# CONFIG_X86_PAE is not set
 # CONFIG_X86_PCC_CPUFREQ is not set
 CONFIG_X86_PM_TIMER=y
 # CONFIG_X86_POWERNOW_K8 is not set