[docs] Update --spirv-max-version allowed values

Original commit:
KhronosGroup/SPIRV-LLVM-Translator@ef0015c

Author: svenvh

llvm-spirv/README.md

@@ -173,7 +173,7 @@ the version of the SPIR-V file which is being generated/consumed.
   the input file and emit an error if the SPIR-V version in it is higher than
   one specified via this option.
 
-Allowed values are `1.0`/`1.1`.
+Allowed values are `1.0`, `1.1`, `1.2`, `1.3`, and `1.4`.
 
 More information can be found in
 [SPIR-V versions and extensions handling](docs/SPIRVVersionsAndExtensionsHandling.rst)

llvm-spirv/docs/SPIRVVersionsAndExtensionsHandling.rst

@@ -65,7 +65,7 @@ the version of the SPIR-V file which is being generated/consumed.
   one exception: resulting SPIR-V version cannot be raised higher than
   specified by this option.
 
-Allowed values are ``1.0`` and ``1.1``.
+Allowed values are ``1.0``, ``1.1``, ``1.2``, ``1.3``, and ``1.4``.
 
 .. warning::
    These two options are mutually exclusive and cannot be specified at the