semihosting/arm-compat: Include missing 'cpu.h' header

ARM semihosting implementations in "common-semi-target.h"
must de-reference the target CPUArchState, which is declared
in each target "cpu.h" header. Include it in order to avoid
when refactoring:

  In file included from ../../semihosting/arm-compat-semi.c:169:
  ../target/riscv/common-semi-target.h:16:5: error: use of undeclared identifier 'RISCVCPU'
     16 |     RISCVCPU *cpu = RISCV_CPU(cs);
        |     ^

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20250103171037.11265-4-philmd@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20250116160306.1709518-6-alex.bennee@linaro.org>

semihosting/arm-compat-semi.c

@@ -166,6 +166,7 @@ static LayoutInfo common_semi_find_bases(CPUState *cs)
 
 #endif
 
+#include "cpu.h"
 #include "common-semi-target.h"
 
 /*