Update MySQL with Solaris 11 IPS Package
There's a couple things that may be going on here (possibly both):


In a fresh install, the default package repository is set to http://pkg.oracle.com/solaris/release/ which contains the packages from the initial Solaris 11.3 release in 2015.  To get updates you need to switch to the /support repo, which is only available to customers with a current support contract.  See How to Update Oracle Solaris 11 Systems From Oracle Support Repositories for instructions.
The packages provided with Solaris, like MySQL, default to being updated only as part of an OS update, not individually.  You may be able to unlock them to allow changing versions independently when needed - this is described in More Tips for Updating Your Oracle Solaris 11 System from the Oracle Support Repository under "Updating an Individual Package" or in Relaxing Version Constraints Specified by Constraint Packages.