package/xenomai: smp support needs at least armv6

There are no autobuilder failures for this issue, but the following
defconfig:

BR2_arm=y
BR2_TOOLCHAIN_EXTERNAL=y
BR2_PACKAGE_XENOMAI=y
BR2_PACKAGE_XENOMAI_COBALT=y

See:
https://gitlab.denx.de/Xenomai/xenomai/-/blob/v3.1/lib/cobalt/arch/arm/include/asm/xenomai/features.h#L56

Signed-off-by: Romain Naour <romain.naour@gmail.com>
[yann.morin.1998@free.fr: fix the condition]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit cb380c2e1155a295919aec122788d046b34e45f0)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/xenomai/Config.in

@@ -84,6 +84,8 @@ endchoice
 config BR2_PACKAGE_XENOMAI_ENABLE_SMP
 	bool "Enable SMP support"
 	default y
+	# SMP not supported below armv6
+	depends on !BR2_ARM_CPU_ARMV4 && !BR2_ARM_CPU_ARMV5
 	help
 	  This option enables SMP support in Xenomai userspace.