[AArch64][GlobalISel] NFC: Replace IR regbankselect test with MIR test

regbank-ceil.ll -> regbank-ceil.mir

The IR test was intended to only check register banks. This makes it brittle,
especially as we improve load/store combines in GlobalISel.

Rewriting this as a MIR test also makes it more consistent with the rest of
the testcases in GlobalISel.

llvm/test/CodeGen/AArch64/GlobalISel/regbank-ceil.mir

@@ -0,0 +1,26 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple=aarch64 -run-pass=regbankselect -verify-machineinstrs %s -o - | FileCheck %s
+
+...
+---
+name:            load_gets_fpr
+legalized:       true
+regBankSelected: false
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $x0
+    ; CHECK-LABEL: name: load_gets_fpr
+    ; CHECK: liveins: $x0
+    ; CHECK: %ptr:gpr(p0) = COPY $x0
+    ; CHECK: %load:fpr(s32) = G_LOAD %ptr(p0) :: (load 4)
+    ; CHECK: %fceil:fpr(s32) = G_FCEIL %load
+    ; CHECK: $s0 = COPY %fceil(s32)
+    ; CHECK: RET_ReallyLR implicit $s0
+    %ptr:_(p0) = COPY $x0
+    %load:_(s32) = G_LOAD %ptr(p0) :: (load 4)
+    %fceil:_(s32) = G_FCEIL %load
+    $s0 = COPY %fceil:_(s32)
+    RET_ReallyLR implicit $s0
+
+...