Maintainers.txt: Update maintainers list

Maintainers.txt: Update maintainers list

Update package maintainers for below package/arch,

1. RISCV64 Architecture:
   Abner is stepping out from RISC-V stuff for now and hand over edk2 RISC-V
   responsibilities to Sunil.
   Daniel Schaefer is no longer with HPE. Update his email address for
   RISCV64 arch. He will keep helping on RISC-V stuff with his personal
   email.

2. EmbeddedPkg:
   Daniel Schaefer is no longer with HPE. Update his email address for
   EmbeddedPkg.

3. EmulatorPkg and RedfishPkg:
   Nickle Wang is no longer with HPE. Update his email address for
   EmulatorPkg and RedfishPkg packages. He will use the personal email for
   the time being until he gets ready with his next journey.

Signed-off-by: Abner Chang <abner.chang@amd.com>
Cc: Andrew Fish <afish@apple.com>
Cc: Leif Lindholm <quic_llindhol@quicinc.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Daniel Schaefer <git@danielschaefer.me>
Cc: Sunil V L <sunilvl@ventanamicro.com>
Cc: Nickle Wang <nickle@csie.io>
Reviewed-by: Daniel Schaefer <git@danielschaefer.me>
Reviewed-by: Sunil V L <sunilvl@ventanamicro.com>
Reviewed-by: Nickle Wang <nickle@csie.io>
Reviewed-by: Leif Lindholm <quic_llindhol@quicinc.com>