arch: add the basic IBM s390x and Z arch support

Signed-off-by: Alexander Egorenkov <egorenar@linux.ibm.com>
[yann.morin.1998@free.fr: drop supperfluous depends on s390x in choice]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

DEVELOPERS

@@ -147,6 +147,9 @@ N:	Alexander Egorenkov <egorenar-dev@posteo.net>
 F:	package/makedumpfile/
 F:	package/multipath-tools/
 
+N:	Alexander Egorenkov <egorenar@linux.ibm.com>
+F:	arch/Config.in.s390x
+
 N:	Alexander Kurz <akurz@blala.de>
 F:	package/minimodem/
 

Makefile

@@ -445,6 +445,7 @@ KERNEL_ARCH := $(shell echo "$(ARCH)" | sed -e "s/-.*//" \
 	-e s/ppc.*/powerpc/ -e s/mips.*/mips/ \
 	-e s/riscv.*/riscv/ \
 	-e s/sh.*/sh/ \
+	-e s/s390x/s390/ \
 	-e s/microblazeel/microblaze/)
 
 ZCAT := $(call qstrip,$(BR2_ZCAT))

arch/Config.in

@@ -219,6 +219,16 @@ config BR2_riscv
 	  https://riscv.org/
 	  https://en.wikipedia.org/wiki/RISC-V
 
+config BR2_s390x
+	bool "s390x"
+	select BR2_ARCH_IS_64
+	select BR2_ARCH_HAS_MMU_MANDATORY
+	select BR2_ARCH_HAS_NO_TOOLCHAIN_BUILDROOT
+	help
+	  s390x is a big-endian architecture made by IBM.
+	  http://www.ibm.com/
+	  http://en.wikipedia.org/wiki/IBM_System/390
+
 config BR2_sh
 	bool "SuperH"
 	select BR2_ARCH_HAS_MMU_OPTIONAL
@@ -457,6 +467,10 @@ if BR2_riscv
 source "arch/Config.in.riscv"
 endif
 
+if BR2_s390x
+source "arch/Config.in.s390x"
+endif
+
 if BR2_sh
 source "arch/Config.in.sh"
 endif

arch/Config.in.s390x

@@ -0,0 +1,33 @@
+
+choice
+	prompt "Target Architecture Variant"
+	help
+	  Specific CPU variant to use
+
+config BR2_s390x_z13
+	bool "z13"
+	depends on BR2_s390x
+
+config BR2_s390x_z14
+	bool "z14"
+	depends on BR2_s390x
+
+config BR2_s390x_z15
+	bool "z15"
+	depends on BR2_s390x
+
+endchoice
+
+config BR2_ARCH
+	default "s390x"	if BR2_s390x
+
+config BR2_ENDIAN
+	default "BIG"
+
+config BR2_GCC_TARGET_ARCH
+	default "arch11" if BR2_s390x_z13
+	default "arch12" if BR2_s390x_z14
+	default "arch13" if BR2_s390x_z15
+
+config BR2_READELF_ARCH_NAME
+	default "IBM S/390"	if BR2_s390x