selftests/powerpc: Fix 32-bit BE build errors on Ubuntu 24.04

Starting with Ubuntu 24.04, building the selftests with the big endian
compiler (which defaults to 32-bit) fails with errors:

  stack_expansion_ldst.c:178:37: error: format '%lx' expects argument
  of type 'long unsigned int', but argument 2 has type 'rlim_t' {aka 'long long unsigned int'}
  subpage_prot.c:214:38: error: format '%lx' expects argument of type
  'long unsigned int', but argument 3 has type 'off_t' {aka 'long long int'}

Prior to 24.04 rlim_t was long unsigned int, and off_t was long int.

Cast to unsigned long long and long long before passing to printf to
avoid the errors.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/20241106130453.1741013-3-mpe@ellerman.id.au