ceph.spec.in, debian/rules: Set rbd-rwl-cache optional on arm64 and ppc64le

ceph.spec.in, debian/rules: Set rbd-rwl-cache optional on arm64 and ppc64le

set rwl cache option on arm64 and ppc64le as PMDK is not well supported.
Currently, only 64-bit Linux* and Windows* on x86 are supported PMDK

Reference:
1. Experimental support on Arm64, but lacking of librpmem:
See: https://github.com/pmem/pmdk#experimental-support-for-64-bit-arm
2. No RPM for PMDK on Arm64:
See: https://bugzilla.redhat.com/show_bug.cgi?id=1340635
3. > Does PMDK support ARM64*?
   > Currently only 64-bit Linux* and Windows* on x86 are supported.
See: https://software.intel.com/content/www/us/en/develop/articles/persistent-memory-faq.html
4. Make check fail on Arm64
See: https://github.com/pmem/pmdk/issues/5255

Fixes: https://tracker.ceph.com/issues/51339
Signed-off-by: Kevin Zhao <kevin.zhao@linaro.org>