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

uc.c

@@ -380,14 +380,12 @@ uc_err uc_reg_read(uc_engine *uc, int regid, void *value)
     return uc_reg_read_batch(uc, &regid, &value, 1);
 }
 
-
 UNICORN_EXPORT
 uc_err uc_reg_write(uc_engine *uc, int regid, const void *value)
 {
     return uc_reg_write_batch(uc, &regid, (void *const *)&value, 1);
 }
 
-
 // check if a memory area is mapped
 // this is complicated because an area can overlap adjacent blocks
 static bool check_mem_area(uc_engine *uc, uint64_t address, size_t size)