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

bindings/python/unicorn/x86_const.py

@@ -250,7 +250,8 @@ UC_X86_REG_LDTR = 244
 UC_X86_REG_TR = 245
 UC_X86_REG_FPCW = 246
 UC_X86_REG_FPTAG = 247
-UC_X86_REG_ENDING = 248
+UC_X86_REG_MSR = 248
+UC_X86_REG_ENDING = 249
 
 # X86 instructions