xen/arm: Update silicon-errata.txt with the Neovers AT erratum

Commit 858c0be8c2 "xen/arm: Enable CPU Erratum 1165522 for Neoverse"
added a new erratum but forgot to update silicon-errata.txt.

Update the file accordingly to keep track of errata workaround in Xen.

Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>

docs/misc/arm/silicon-errata.txt

@@ -51,4 +51,5 @@ stable hypervisors.
 | ARM            | Cortex-A57      | #1319537        | N/A                     |
 | ARM            | Cortex-A72      | #1319367        | N/A                     |
 | ARM            | Cortex-A76      | #1165522        | N/A                     |
+| ARM            | Neoverse-N1     | #1165522        | N/A
 | ARM            | MMU-500         | #842869         | N/A                     |