gpu: ion: Clarify variable names and comments around heap ids v types

There is some confusion between when to use the heap type and when
the id.  This patch clarifies this by using clearer variable names
and describing the intention in the comments.  Also fixes the client
debug code to print heaps by id instead of type.

Change-Id: I0c1903ed7bf748ac4b1f2c4235e4d31d6a906f2d
Signed-off-by: Rebecca Schultz Zavin <rebecca@android.com>
Git-commit: ac3da7344f52f727e833593ce547c7d60fa42074
Git-repo: https://android.googlesource.com/kernel/common


[lauraa@codeaurora.org: Minor context differences due to more
debugging output and debugfs differences. Need to change some
debug prints. Dropping changing the name of the userspace field
until we can synchronize all clients later]
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>