base: ELF segment types are not bitfields.

base: ELF segment types are not bitfields.

The ELF segment type had been checked by bitwise &-ing it with the
PT_LOAD constant to check if it was loadable. This is incorrect. The
value is a flat integer, with different values selecting different
types of segments.

Change-Id: I644dd985bda4ad2d992557c90ffe8048c0ae6aac
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21460
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com>