KVM: x86 emulator: adds support to mov r,imm (opcode 0xb8) instruction

Add support to mov r, imm (0xb8) instruction.

Signed-off-by: Guillaume Thouvenin <guillaume.thouvenin@ext.bull.net>
Signed-off-by: Laurent Vivier <laurent.vivier@bull.net>
Signed-off-by: Avi Kivity <avi@qumranet.com>