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>

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