tmem: cleanup: rename 'tmh_' with 'tmem_'

tmem: cleanup: rename 'tmh_' with 'tmem_'

tmem was designed can be ported to other platform besides xen easily, but I
don't think anybody will port tmem to other platform. And this flexible
character made tmem not easy for understand, there are too many 'tmh_' and
'tmem_' functions and variables.

This patch replace all 'tmh_' functions/variables with 'tmem_' to make code
more readable.

Signed-off-by: Bob Liu <bob.liu@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>