feat(pm_low_power_modes): Note AM62-LP LPM fails when connected to USB

Denote that SK-AM62-LP EVM cannot have USB connected when entering LPM,
or the board will fail to resume to Linux.

Signed-off-by: Kendall Willis <k-willis@ti.com>

Author: kwillis01

source/linux/Foundational_Components/Power_Management/pm_low_power_modes.rst

@@ -387,6 +387,12 @@ Limitations
 
       SK-AM62-SIP EVM does NOT support low power modes.
 
+   .. important::
+
+      When using low power modes on SK-AM62-LP EVM, USB **cannot** be connected
+      to anything. When USB is connected and a low power mode is entered, the
+      EVM fails to resume to an active Linux state.
+
 HWRNG support on GP devices is incompatible with Deep Sleep and MCU Only
 modes. To test LPM on GP devices, HWRNG has to be unloaded one-time
 before running the Suspend-to-RAM command: