[GAS][AARCH64]Fix a typo for IP1 register alias.

[Nick Clifton]

Hi Renlin,

> This should be an obvious fix.

It is.

> gas/ChangeLog:
> 2017-11-29  Renlin Li  <renlin.li@arm.com>
> 
> Â Â Â Â * config/tc-aarch64.c (reg_names): Fix IP1 register alias error.
> Â Â Â Â * testsuite/gas/aarch64/register_aliases.s: Add IP0 and IP1 tests.
> Â Â Â Â * testsuite/gas/aarch64/register_aliases.d: Update.

Approved, please apply.

Cheers
  Nick