Apply workarounds for A53 Cat A Errata 835769 and 843419

Apply workarounds for A53 Cat A Errata 835769 and 843419

These errata are only applicable to AArch64 state. See the errata notice
for more details:
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.epm048406/index.html

Introduce the build options ERRATA_A53_835769 and ERRATA_A53_843419.
Enable both of them for Juno.

Apply the 835769 workaround as following:
* Compile with -mfix-cortex-a53-835769
* Link with --fix-cortex-a53-835769

Apply the 843419 workaround as following:
* Link with --fix-cortex-a53-843419

The erratum 843419 workaround can lead the linker to create new sections
suffixed with "*.stub*" and 4KB aligned. The erratum 835769 can lead the
linker to create new "*.stub" sections with no particular alignment.

Also add support for LDFLAGS_aarch32 and LDFLAGS_aarch64 in Makefile for
architecture-specific linker options.

Change-Id: Iab3337e338b7a0a16b0d102404d9db98c154f8f8
Signed-off-by: Douglas Raillard <douglas.raillard@arm.com>