package/xen: security bump to version 4.11.2

package/xen: security bump to version 4.11.2

The 4.11.2 release brings a large number of fixes:

https://xenproject.org/downloads/xen-project-archives/xen-project-4-11-series/xen-project-4-11-2/

Including a number of security fixes:

XSA-284: grant table transfer issues on large hosts
XSA-285: race with pass-through device hotplug
XSA-287: x86: steal_page violates page_struct access discipline
XSA-288: x86: Inconsistent PV IOMMU discipline
XSA-290: missing preemption in x86 PV page table unvalidation
XSA-291: x86/PV: page type reference counting issue with failed IOMMU update
XSA-292: x86: insufficient TLB flushing when using PCID
XSA-293: x86: PV kernel context switch corruption
XSA-294: x86 shadow: Insufficient TLB flushing when using PCID
XSA-295: Unlimited Arm Atomics Operations
XSA-297: Microarchitectural Data Sampling speculative side channel

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>