MAINTAINERS: Update Lorenzo Pieralisi's email address

I will soon lose my @arm.com email address, so to prevent any possible
issue let's update all kernel references (inclusive of .mailmap) to my
@kernel.org alias ahead of time.

My @arm.com address is still working and will likely resume to work at some
point in the future; nonetheless, it is safer to switch to the @kernel.org
alias from now onwards so that continuity is guaranteed.

Link: https://lore.kernel.org/r/20220528151411.29810-1-lorenzo.pieralisi@arm.com


Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>