x86: add MSR API via reg API (#755)

Writing / reading to model specific registers should be as easy as
calling a function, it's a bit stupid to write shell code and run them
just to write/read to a MSR, and even worse, you need more than just a
shellcode to read...

So, add a special register ID called UC_X86_REG_MSR, which should be
passed to uc_reg_write()/uc_reg_read() as the register ID, and then a
data structure which is uc_x86_msr (12 bytes), as the value (always), where:
	Byte	Value		Size
	0	MSR ID		4
	4       MSR val		8

include/uc_priv.h

@@ -251,3 +251,4 @@ struct uc_context {
 MemoryRegion *memory_mapping(struct uc_struct* uc, uint64_t address);
 
 #endif
+/* vim: set ts=4 noet:  */