arm: Restore the names of fields in fpreg structure

[kd]

Summary

While adding the support for using VFP in the kernel the layout/names of fields of the fpreg structure was changed, which broke compilation of the libunwind port.
Work around that by restoring previous names of the fields.
Note that the layout still remains changed.
Before we'd only have 8 FP registers, and that's the amount libunwind expects.
In reality there are 32 of them, take that into account.

[andrew]

Upstream libunwind already changed to the new name in https://github.com/libunwind/libunwind/commit/99fb31d5f05ff6c96ca3a9350c792618fab23f2d

[kd]

In D39364#896033, @andrew wrote:

Upstream libunwind already changed to the new name in https://github.com/libunwind/libunwind/commit/99fb31d5f05ff6c96ca3a9350c792618fab23f2d

Hmm, right.
So I guess that it's better to leave it as is.
We need to update our port though.

[markmi_dsl-only.net]

Port is still mismatched for armv7 as of:

# ~/fbsd-based-on-what-commit.sh -C /usr/ports/
3712f30953d5 (HEAD -> main, freebsd/main, freebsd/HEAD) devel/fnc: Update to 0.15
Author:     Ashish SHUKLA <[e-mail]>
Commit:     Ashish SHUKLA <[e-mail]>
CommitDate: 2023-04-29 20:35:45 +0000
branch: main
merge-base: 3712f30953d5dadb3fede83e2e780024fb883a65
merge-base: CommitDate: 2023-04-29 20:35:45 +0000
n617500 (--first-parent --count for merge-base)

Details:

--- ptrace/_UPT_access_fpreg.lo ---
ptrace/_UPT_access_fpreg.c:110:25: error: no member named 'fpr' in 'struct fpreg'
          memcpy(&fpreg.fpr[reg], val, sizeof(unw_fpreg_t));
                  ~~~~~ ^
ptrace/_UPT_access_fpreg.c:126:30: error: no member named 'fpr' in 'struct fpreg'
          memcpy(val, &fpreg.fpr[reg], sizeof(unw_fpreg_t));
                       ~~~~~ ^
2 errors generated.