KVM: arm64: Introduce struct kvm_s2_fault to user_mem_abort()

KVM: arm64: Introduce struct kvm_s2_fault to user_mem_abort()

The user_mem_abort() function takes many arguments and defines a large
number of local variables. Passing all these variables around to helper
functions would result in functions with too many arguments.

Introduce struct kvm_s2_fault to encapsulate the stage-2 fault state.
This structure holds both the input parameters and the intermediate
state required during the fault handling process.

Update user_mem_abort() to initialize this structure and replace the
usage of local variables with fields from the new structure.

This prepares the ground for further extracting parts of
user_mem_abort() into smaller helper functions that can simply take a
pointer to the fault state structure.

Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Signed-off-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>