Remove unnecessarily allowed zeros; Fix RISC-V

Author: jzadnik

sycl/doc/design/spirv-extensions/targets/architectures.asciidoc

@@ -7,14 +7,6 @@
 |Value
 |Description
 
-a|
-[source]
-----
-unknown
-----
-| 0
-| Unknown category
-
 a|
 [source]
 ----
@@ -49,17 +41,6 @@ npu
 |Value
 |Description
 
-4+^|*Category: unknown (0)*
-
-a|
-[source]
-----
-generic
-----
-| 0
-| 0
-| Generic family
-
 4+^|*Category: cpu (1)*
 
 a|
@@ -347,18 +328,6 @@ amd_xdna
 |Value
 |Description
 
-5+^|*Category: unknown (0), Family: generic (0)*
-
-a|
-[source]
-----
-any
-----
-| 0
-| 0
-| 0
-| Any architecture
-
 5+^|*Category: cpu (1), Family: generic (0)*
 
 a|