docs/devel/tcg-ops: Bury mentions of trunc_shr_i64_i32()

Commit 609ad705 ("tcg: Split trunc_shr_i32 opcode into
extr[lh]_i64_i32") remove trunc_shr_i64_i32(). Update the
backend documentation.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230822162847.71206-1-philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

docs/devel/tcg-ops.rst

@@ -882,14 +882,15 @@ sub2_i32, brcond2_i32).
 On a 64 bit target, the values are transferred between 32 and 64-bit
 registers using the following ops:
 
-- trunc_shr_i64_i32
+- extrl_i64_i32
+- extrh_i64_i32
 - ext_i32_i64
 - extu_i32_i64
 
 They ensure that the values are correctly truncated or extended when
 moved from a 32-bit to a 64-bit register or vice-versa. Note that the
-trunc_shr_i64_i32 is an optional op. It is not necessary to implement
-it if all the following conditions are met:
+extrl_i64_i32 and extrh_i64_i32 are optional ops. It is not necessary
+to implement them if all the following conditions are met:
 
 - 64-bit registers can hold 32-bit values
 - 32-bit values in a 64-bit register do not need to stay zero or