target/i386: fix memory opsize for Mov to/from Seg

target/i386: fix memory opsize for Mov to/from Seg

This commit fixes an issue with MOV instructions (0x8C and 0x8E)
involving segment registers; MOV to segment register's source is
16-bit, while MOV from segment register has to explicitly set the
memory operand size to 16 bits.  Introduce a new flag
X86_SPECIAL_Op0_Mw to handle this specification correctly.

Signed-off-by: Xinyu Li <lixinyu20s@ict.ac.cn>
Message-ID: <20240602100528.2135717-1-lixinyu20s@ict.ac.cn>
Fixes: 5e9e21bcc4d ("target/i386: move 60-BF opcodes to new decoder", 2024-05-07)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>