gdb/testsuite: Add require allow_hipcc_tests in gdb.rocm/mi-attach.exp

gdb/testsuite: Add require allow_hipcc_tests in gdb.rocm/mi-attach.exp

The gdb.rocm/mi-attach.exp test is missing a proper `require` check to
ensure that the current configuration can run ROCm tests.  This issue
has been reported by Baris.

This patch adds the missing `allow_hipcc_tests` requirement, and also
adds `load_lib rocm.exp` to enable this test.

Change-Id: Ie136adfc2d0854268b92af5c4df2dd0334dce259
Reviewed-By: Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
Approved-By: Tom Tromey <tom@tromey.com>