app: aboot: Modify the integer overflow check
app: aboot: Modify the integer overflow check

If the code is compiled on an architecture which supports 64-bit integer
primitive, then the start and size will be promoted to 64-bit integers
and hence overflow will not be detected. So modify the boundary check to
detect integer overflow.

CRs-Fixed: 590434
Change-Id: I1f93972c12d155f8d06dd6aeedd3e8f2ea09c2f1

t2m-foxfone/android_kernel_lk,t2m-foxfone/android_kernel_lk,lg-devs/g2-bootloader,lg-devs/g2-bootloader,lg-devs/g2-bootloader,t2m-foxfone/android_kernel_lk,t2m-foxfone/android_kernel_lk,mozilla-b2g/fairphone2_kernel_lk,mozilla-b2g/fairphone2_kernel_lk,mozilla-b2g/fairphone2_kernel_lk,mozilla-b2g/fairphone2_kernel_lk,lg-devs/g2-bootloader,lg-devs/g2-bootloader,mozilla-b2g/fairphone2_kernel_lk,t2m-foxfone/android_kernel_lk