spirv/nir: add capability check for SpvCapabilityAtomicStorage

Capability that informs if atomic counters are supported. From SPIR-V
1.0 spec, section 3.7, "Storage Class", item 10 from table:

(Column "Storage Class"):

   "AtomicCounter For holding atomic counters. Visible across all
    functions of the current invocation. Atomic counter-specific
    memory."

(Column "Required Capability"):

   "AtomicStorage"

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

src/compiler/shader_info.h

@@ -57,6 +57,7 @@ struct spirv_supported_capabilities {
    bool descriptor_array_dynamic_indexing;
    bool runtime_descriptor_array;
    bool stencil_export;
+   bool atomic_storage;
 };
 
 typedef struct shader_info {