[RISCV][NFC] Ensure files end with newline. (#154457)

Add trailing newlines to the following files to comply with POSIX
standards:
- llvm/lib/Target/RISCV/RISCVInstrInfoXSpacemiT.td
- llvm/test/MC/RISCV/xsmtvdot-invalid.s
- llvm/test/MC/RISCV/xsmtvdot-valid.s

Closes #151706

Author: link-xyq

llvm/lib/Target/RISCV/RISCVInstrInfoXSpacemiT.td

@@ -136,4 +136,4 @@ def SMT_VMADOT3U  : RVInstSMTVDotSlide<SMT_VDot_Slide3, SMT_VDot_UU, "smt.vmadot
 def SMT_VMADOT3SU : RVInstSMTVDotSlide<SMT_VDot_Slide3, SMT_VDot_SU, "smt.vmadot3su", "$vd, $vs1, $vs2">;
 def SMT_VMADOT3US : RVInstSMTVDotSlide<SMT_VDot_Slide3, SMT_VDot_US, "smt.vmadot3us", "$vd, $vs1, $vs2">;
 }
-}
+} // DecoderNamespace = "XSMT"

llvm/test/MC/RISCV/xsmtvdot-invalid.s

@@ -49,4 +49,4 @@ smt.vmadot3us v2, v1, v2 # CHECK: :[[@LINE]]:19: error: invalid operand for inst
 smt.vmadot3   v1, v3, v2 # CHECK: :[[@LINE]]:15: error: invalid operand for instruction
 smt.vmadot3u  v1, v3, v2 # CHECK: :[[@LINE]]:15: error: invalid operand for instruction
 smt.vmadot3su v1, v3, v2 # CHECK: :[[@LINE]]:15: error: invalid operand for instruction
-smt.vmadot3us v1, v3, v2 # CHECK: :[[@LINE]]:15: error: invalid operand for instruction
+smt.vmadot3us v1, v3, v2 # CHECK: :[[@LINE]]:15: error: invalid operand for instruction

llvm/test/MC/RISCV/xsmtvdot-valid.s

@@ -111,4 +111,4 @@ smt.vmadot3su v12, v4, v10
 # CHECK-ENCODING: [0x2b,0x97,0xb3,0xe6]
 # CHECK-ERROR: instruction requires the following: 'XSMTVDot' (SpacemiT Vector Dot Product Extension){{$}}
 # CHECK-UNKNOWN: e6b3972b <unknown>
-smt.vmadot3us v14, v6, v11
+smt.vmadot3us v14, v6, v11