mailmap: Update email for Punit Agrawal

As I'll no longer be working with Arm, add a mailmap entry so any mail
directed towards me reaches the appropriate mailbox.
Acked-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NPunit Agrawal <punit.agrawal@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

.mailmap

@@ -159,6 +159,7 @@ Peter Oruba <peter@oruba.de>
 Peter Oruba <peter.oruba@amd.com>
 Pratyush Anand <pratyush.anand@gmail.com> <pratyush.anand@st.com>
 Praveen BP <praveenbp@ti.com>
+Punit Agrawal <punitagrawal@gmail.com> <punit.agrawal@arm.com>
 Qais Yousef <qsyousef@gmail.com> <qais.yousef@imgtec.com>
 Oleksij Rempel <linux@rempel-privat.de> <bug-track@fisher-privat.net>
 Oleksij Rempel <linux@rempel-privat.de> <external.Oleksij.Rempel@de.bosch.com>