KVM: selftests: Add atoi_positive() and atoi_non_negative() for input validation

KVM: selftests: Add atoi_positive() and atoi_non_negative() for input validation

Many KVM selftests take command line arguments which are supposed to be
positive (>0) or non-negative (>=0). Some tests do these validation and
some missed adding the check.

Add atoi_positive() and atoi_non_negative() to validate inputs in
selftests before proceeding to use those values.

Signed-off-by: Vipin Sharma <vipinsh@google.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20221103191719.1559407-7-vipinsh@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>