cmd_arm64 function failure

[dkmcgrath]

With the current code in cmd_arm64, when trying to use the arm64 command, I get:

keystone.keystone.KsError: Invalid mode (KS_ERR_MODE)

The reason for this seems to be a change in keystone-engine (I think).

The offending code is

assemble_keystone(keystone.KS_ARCH_ARM64, keystone.KS_MODE_ARM, inst_list)

I believe it should be

assemble_keystone(keystone.KS_ARCH_ARM64, keystone.KS_MODE_LITTLE_ENDIAN, inst_list)

I'm not sure if this is a keystone issue or an issue with lldbinit.