docs: amu: supress some Sphinx warnings

Add extra blank lines on some places, in order to avoid those
warnings when building the docs:

    Documentation/arm64/amu.rst:26: WARNING: Unexpected indentation.
    Documentation/arm64/amu.rst:60: WARNING: Unexpected indentation.
    Documentation/arm64/amu.rst:81: WARNING: Unexpected indentation.
    Documentation/arm64/amu.rst:108: WARNING: Unexpected indentation.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/ab0881638fc41ed790b3307a8e022ec84b7cce7e.1586881715.git.mchehab+huawei@kernel.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/arm64/amu.rst

@@ -23,6 +23,7 @@ optional external memory-mapped interface.
 
 Version 1 of the Activity Monitors architecture implements a counter group
 of four fixed and architecturally defined 64-bit event counters.
+
   - CPU cycle counter: increments at the frequency of the CPU.
   - Constant counter: increments at the fixed frequency of the system
     clock.
@@ -57,6 +58,7 @@ counters, only the presence of the extension.
 
 Firmware (code running at higher exception levels, e.g. arm-tf) support is
 needed to:
+
  - Enable access for lower exception levels (EL2 and EL1) to the AMU
    registers.
  - Enable the counters. If not enabled these will read as 0.
@@ -78,6 +80,7 @@ are not trapped in EL2/EL3.
 
 The fixed counters of AMUv1 are accessible though the following system
 register definitions:
+
  - SYS_AMEVCNTR0_CORE_EL0
  - SYS_AMEVCNTR0_CONST_EL0
  - SYS_AMEVCNTR0_INST_RET_EL0
@@ -93,6 +96,7 @@ Userspace access
 ----------------
 
 Currently, access from userspace to the AMU registers is disabled due to:
+
  - Security reasons: they might expose information about code executed in
    secure mode.
  - Purpose: AMU counters are intended for system management use.
@@ -105,6 +109,7 @@ Virtualization
 
 Currently, access from userspace (EL0) and kernelspace (EL1) on the KVM
 guest side is disabled due to:
+
  - Security reasons: they might expose information about code executed
    by other guests or the host.