arch/arm: add the Cortex-A710 core

This commit adds the Cortex-A710 core, which is an implementation of
the armv9.0a ISA. See: [1] [2].

This CPU support was added in GCC 12. See [3] [4].

Cortex-A710 support has been added in QEmu in commit [5], first
included in v8.2.0.

This CPU supports Aarch32 only in EL0 (user-space). This means it's
technically possible to compile Aarch32 code targeting. GCC has the
support to do so. Since Buildroot recompiles a full system (ATF,
Kernel, user-space) this support has limited value. This is why this
CPU is limited  to 64bit builds only.

[1] https://developer.arm.com/Processors/Cortex-A710
[2] https://developer.arm.com/documentation/101800/0201/The-Cortex-A710--core/Cortex-A710--core-features
[3] https://gcc.gnu.org/gcc-12/changes.html
[4] https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/config/aarch64/aarch64-cores.def;hb=releases/gcc-12.1.0#l163
[5] e3d45c0a89

Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

arch/Config.in.arm

@@ -506,6 +506,12 @@ config BR2_saphira
 	select BR2_ARCH_NEEDS_GCC_AT_LEAST_8
 
 comment "armv9.0a cores"
+config BR2_cortex_a710
+	bool "Cortex-A710 (aka matterhorn)"
+	depends on BR2_ARCH_IS_64
+	select BR2_ARM_CPU_HAS_FP_ARMV8
+	select BR2_ARM_CPU_ARMV9A
+	select BR2_ARCH_NEEDS_GCC_AT_LEAST_12
 config BR2_neoverse_n2
 	bool "neoverse-N2 (aka perseus)"
 	depends on BR2_ARCH_IS_64
@@ -906,6 +912,7 @@ config BR2_GCC_TARGET_CPU
 	# armv8.4a
 	default "saphira"	if BR2_saphira
 	# armv9.0a
+	default "cortex-a710"	if BR2_cortex_a710
 	default "neoverse-n2"	if BR2_neoverse_n2
 
 config BR2_GCC_TARGET_ABI