xen: allow up to 16383 cpus

With lock handling now allowing up to 16384 cpus (spinlocks can handle
65535 cpus, rwlocks can handle 16384 cpus), raise the allowed limit for
the number of cpus to be configured to 16383.

The new limit is imposed by IOMMU_CMD_BUFFER_MAX_ENTRIES and
QINVAL_MAX_ENTRY_NR required to be larger than 2 * CONFIG_NR_CPUS.

Add a support limit of physical CPUs to SUPPORT.md (4096 on x86, 128
on ARM).

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Julien Grall <jgrall@amazon.com>

SUPPORT.md

@@ -61,6 +61,11 @@ For the Cortex A77 r0p0 - r1p0, see Errata 1508412.
 
     Status, x86: Supported
 
+### Physical CPUs
+
+    Status, x86: Supported up to 4096
+    Status, ARM: Supported up to 128
+
 ### Host ACPI (via Domain 0)
 
     Status, x86 PV: Supported