exclude svnapot and fix errors logged from ruamel.

Signed-off-by: Karthik B K <karthik.bk@incoresemi.com>

the get_march_mabi function should return a string that
can be consumed by the riscv-gcc right away. the compiler
complains about the presence of svnapot in the said string.
"nullify" this extension, resulting in exclusion during march generation.

Signed-off-by: Karthik B K <karthik.bk@incoresemi.com>

the load_yaml function performs a bit of post-processing
on the error message obtained from the ruamel constructor.
log the raw error message until the post-processing is corrected.

Signed-off-by: Karthik B K <karthik.bk@incoresemi.com>

Added yaml dump flag

mprv should not be implemented when U mode is absent.

mabi generation to account for E extension

Add ssdbltrp, smdbltrp, sddbltrp

Support march generation without custom extensions

Custom csr fields fix

Added function that returns the march and mabi for gcc from a given ISA