plat/arm: Support direct Linux kernel boot in AArch32

This option allows the Trusted Firmware to directly jump to Linux
kernel for aarch32 without the need of an intermediate loader such
as U-Boot.

Similar to AArch64 ARM_LINUX_KERNEL_AS_BL33 only available with
RESET_TO_SP_MIN=1 as well as BL33 and DTB are preloaded in memory.

Change-Id: I908bc1633696be1caad0ce2f099c34215c8e0633
Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
diff --git a/docs/user-guide.rst b/docs/user-guide.rst
index 52cb45c..a8bd40c 100644
--- a/docs/user-guide.rst
+++ b/docs/user-guide.rst
@@ -728,11 +728,12 @@
 -  ``ARM_LINUX_KERNEL_AS_BL33``: The Linux kernel expects registers x0-x3 to
    have specific values at boot. This boolean option allows the Trusted Firmware
    to have a Linux kernel image as BL33 by preparing the registers to these
-   values before jumping to BL33. This option defaults to 0 (disabled). For now,
-   it  only supports AArch64 kernels. ``RESET_TO_BL31`` must be 1 when using it.
-   If this option is set to 1, ``ARM_PRELOADED_DTB_BASE`` must be set to the
-   location of a device tree blob (DTB) already loaded in memory.  The Linux
-   Image address must be specified using the ``PRELOADED_BL33_BASE`` option.
+   values before jumping to BL33. This option defaults to 0 (disabled). For
+   AArch64 ``RESET_TO_BL31`` and for AArch32 ``RESET_TO_SP_MIN`` must be 1 when
+   using it. If this option is set to 1, ``ARM_PRELOADED_DTB_BASE`` must be set
+   to the location of a device tree blob (DTB) already loaded in memory. The
+   Linux Image address must be specified using the ``PRELOADED_BL33_BASE``
+   option.
 
 -  ``ARM_RECOM_STATE_ID_ENC``: The PSCI1.0 specification recommends an encoding
    for the construction of composite state-ID in the power-state parameter.