Replace enum with fixed-width int in UAPI structs

In order to avoid struct layout misalignment issues between user and
kernel space, raising from size of enum members being implementation-
defined, the enum members of structs in the UAPI header file have now
been replaced with fixed-width integers.

Change-Id: I44a41c6d6669d116ca239da72676dd0539bf88b9
Signed-off-by: Ledion Daja <ledion.daja@arm.com>