powerpc: replace #include <asm/export.h> with #include <linux/export.h>

Commit ddb5cdbafaaa ("kbuild: generate KSYMTAB entries by modpost")
deprecated <asm/export.h>, which is now a wrapper of <linux/export.h>.

Replace #include <asm/export.h> with #include <linux/export.h>.

After all the <asm/export.h> lines are converted, <asm/export.h> and
<asm-generic/export.h> will be removed.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
[mpe: Fixup selftests that stub asm/export.h]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230806150954.394189-2-masahiroy@kernel.org

selftests/powerpc: Add test for 32 bits memcmp

This patch renames memcmp test to memcmp_64 and adds a memcmp_32 test
for testing the 32 bits version of memcmp()

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
[mpe: Fix 64-bit build by adding build_32bit test]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

powerpc/lib: optimise PPC32 memcmp

At the time being, memcmp() compares two chunks of memory
byte per byte.

This patch optimises the comparison by comparing word by word.

On the same way as commit 15c2d45d17418 ("powerpc: Add 64bit
optimised memcmp"), this patch moves memcmp() into a dedicated
file named memcmp_32.S

A small benchmark performed on an 8xx comparing two chuncks
of 512 bytes performed 100000 times gives:

Before : 5852274 TB ticks
After: 1488638 TB ticks

This is almost 4 times faster

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>