update SUPPORT.md for static allocation

SUPPORT.md doesn't seem to explicitly say whether static memory is
supported, so this commit updates SUPPORT.md to add feature static
allocation tech preview for now.

Signed-off-by: Penny Zheng <penny.zheng@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

SUPPORT.md

@@ -286,6 +286,13 @@ to boot with memory < maxmem.
 
     Status, x86 HVM: Supported
 
+### Static Allocation
+
+Static allocation refers to domains for which memory areas are
+pre-defined by configuration using physical address ranges.
+
+    Status, ARM: Tech Preview
+
 ### Memory Sharing
 
 Allow sharing of identical pages between guests