docs/system/arm: Add FEAT_HCX to list of emulated features

In commit 5814d587 we added support for emulating
FEAT_HCX (Support for the HCRX_EL2 register). However we
forgot to add it to the list in emulated.rst. Correct the
omission.

Fixes: 5814d587 ("target/arm: Enable FEAT_HCX for -cpu max")
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220520084320.424166-1-peter.maydell@linaro.org

docs/system/arm/emulation.rst

@@ -29,6 +29,7 @@ the following architecture extensions:
 - FEAT_FRINTTS (Floating-point to integer instructions)
 - FEAT_FlagM (Flag manipulation instructions v2)
 - FEAT_FlagM2 (Enhancements to flag manipulation instructions)
+- FEAT_HCX (Support for the HCRX_EL2 register)
 - FEAT_HPDS (Hierarchical permission disables)
 - FEAT_I8MM (AArch64 Int8 matrix multiplication instructions)
 - FEAT_IDST (ID space trap handling)